Drop the null forgiving operator from generated TestContext getter

The generated getter used CurrentTestContext.Value!.TestContext. A consuming
SDK-style project targeting net462, net472 or net48 defaults to LangVersion 7.3,
where ! is CS8370, so UsesVerify.g.cs failed to compile for exactly the target
frameworks Verify.MSTest ships. The repo never saw it because ProjectDefaults
forces LangVersion=preview.

The generated file carries an <auto-generated /> header, so nullable warnings
are suppressed there regardless.

Author: SimonCropp

src/Verify.MSTest.SourceGenerator.Tests/GlobalNamespaceTests.HasAssemblyAttribute.verified.txt

@@ -14,7 +14,7 @@ partial class Foo
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Verify.MSTest.SourceGenerator", "1.0.0.0")]
   public global::Microsoft.VisualStudio.TestTools.UnitTesting.TestContext TestContext
   {
-    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value!.TestContext;
+    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value.TestContext;
     set => global::VerifyMSTest.Verifier.CurrentTestContext.Value = new global::VerifyMSTest.TestExecutionContext(value, GetType());
   }
 }

src/Verify.MSTest.SourceGenerator.Tests/GlobalNamespaceTests.HasAssemblyAttributeAndCustomTestClassAttribute.verified.txt

@@ -14,7 +14,7 @@ partial class Foo
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Verify.MSTest.SourceGenerator", "1.0.0.0")]
   public global::Microsoft.VisualStudio.TestTools.UnitTesting.TestContext TestContext
   {
-    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value!.TestContext;
+    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value.TestContext;
     set => global::VerifyMSTest.Verifier.CurrentTestContext.Value = new global::VerifyMSTest.TestExecutionContext(value, GetType());
   }
 }

src/Verify.MSTest.SourceGenerator.Tests/GlobalNamespaceTests.HasAttributeOnClass.verified.txt

@@ -14,7 +14,7 @@ partial class Foo
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Verify.MSTest.SourceGenerator", "1.0.0.0")]
   public global::Microsoft.VisualStudio.TestTools.UnitTesting.TestContext TestContext
   {
-    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value!.TestContext;
+    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value.TestContext;
     set => global::VerifyMSTest.Verifier.CurrentTestContext.Value = new global::VerifyMSTest.TestExecutionContext(value, GetType());
   }
 }

src/Verify.MSTest.SourceGenerator.Tests/GlobalNamespaceTests.HasBothAssemblyAndClassAttributes.verified.txt

@@ -14,7 +14,7 @@ partial class Foo
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Verify.MSTest.SourceGenerator", "1.0.0.0")]
   public global::Microsoft.VisualStudio.TestTools.UnitTesting.TestContext TestContext
   {
-    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value!.TestContext;
+    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value.TestContext;
     set => global::VerifyMSTest.Verifier.CurrentTestContext.Value = new global::VerifyMSTest.TestExecutionContext(value, GetType());
   }
 }

src/Verify.MSTest.SourceGenerator.Tests/InheritanceTests.HasAssemblyAttributeAndTestClassInheritance.verified.txt

@@ -14,7 +14,7 @@ partial class Base
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Verify.MSTest.SourceGenerator", "1.0.0.0")]
   public global::Microsoft.VisualStudio.TestTools.UnitTesting.TestContext TestContext
   {
-    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value!.TestContext;
+    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value.TestContext;
     set => global::VerifyMSTest.Verifier.CurrentTestContext.Value = new global::VerifyMSTest.TestExecutionContext(value, GetType());
   }
 }

src/Verify.MSTest.SourceGenerator.Tests/InheritanceTests.HasAssemblyAttributeWithTestClassOnDerivedAndMarkerAttributeOnBase.verified.txt

@@ -14,7 +14,7 @@ partial class Base
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Verify.MSTest.SourceGenerator", "1.0.0.0")]
   public global::Microsoft.VisualStudio.TestTools.UnitTesting.TestContext TestContext
   {
-    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value!.TestContext;
+    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value.TestContext;
     set => global::VerifyMSTest.Verifier.CurrentTestContext.Value = new global::VerifyMSTest.TestExecutionContext(value, GetType());
   }
 }

src/Verify.MSTest.SourceGenerator.Tests/InheritanceTests.HasAttributeOnBaseAndDerivedClasses.verified.txt

@@ -14,7 +14,7 @@ partial class Base
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Verify.MSTest.SourceGenerator", "1.0.0.0")]
   public global::Microsoft.VisualStudio.TestTools.UnitTesting.TestContext TestContext
   {
-    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value!.TestContext;
+    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value.TestContext;
     set => global::VerifyMSTest.Verifier.CurrentTestContext.Value = new global::VerifyMSTest.TestExecutionContext(value, GetType());
   }
 }

src/Verify.MSTest.SourceGenerator.Tests/InheritanceTests.HasAttributeOnBaseClass.verified.txt

@@ -14,7 +14,7 @@ partial class Base
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Verify.MSTest.SourceGenerator", "1.0.0.0")]
   public global::Microsoft.VisualStudio.TestTools.UnitTesting.TestContext TestContext
   {
-    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value!.TestContext;
+    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value.TestContext;
     set => global::VerifyMSTest.Verifier.CurrentTestContext.Value = new global::VerifyMSTest.TestExecutionContext(value, GetType());
   }
 }

src/Verify.MSTest.SourceGenerator.Tests/InheritanceTests.HasAttributeOnDerivedClass.verified.txt

@@ -14,7 +14,7 @@ partial class Derived
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Verify.MSTest.SourceGenerator", "1.0.0.0")]
   public global::Microsoft.VisualStudio.TestTools.UnitTesting.TestContext TestContext
   {
-    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value!.TestContext;
+    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value.TestContext;
     set => global::VerifyMSTest.Verifier.CurrentTestContext.Value = new global::VerifyMSTest.TestExecutionContext(value, GetType());
   }
 }

src/Verify.MSTest.SourceGenerator.Tests/InheritanceTests.HasAttributeOnDerivedClassAndAbstractPropertyManuallyDefinedInBase.verified.txt

@@ -14,7 +14,7 @@ partial class Derived
   [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Verify.MSTest.SourceGenerator", "1.0.0.0")]
   public sealed override global::Microsoft.VisualStudio.TestTools.UnitTesting.TestContext TestContext
   {
-    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value!.TestContext;
+    get => global::VerifyMSTest.Verifier.CurrentTestContext.Value.TestContext;
     set => global::VerifyMSTest.Verifier.CurrentTestContext.Value = new global::VerifyMSTest.TestExecutionContext(value, GetType());
   }
 }