Add analyzer tests

Author: andrewlock

tests/NetEscapades.EnumGenerators.IntegrationTests/.editorconfig

@@ -9,4 +9,5 @@ dotnet_diagnostic.NEEG005.severity = error
 dotnet_diagnostic.NEEG006.severity = error
 dotnet_diagnostic.NEEG007.severity = error
 dotnet_diagnostic.NEEG008.severity = error
-dotnet_diagnostic.NEEG009.severity = error
+dotnet_diagnostic.NEEG009.severity = error
+dotnet_diagnostic.NEEG010.severity = error

tests/NetEscapades.EnumGenerators.IntegrationTests/AnalyzerTests.cs

@@ -121,4 +121,15 @@ public void Neeg009Testing()
 #endif
 #pragma warning restore NEEG009
     }
+
+#if NET7_0_OR_GREATER
+    [Fact]
+    public void Neeg010Testing()
+    {
+#pragma warning disable NEEG010
+        _ = Enum.GetValuesAsUnderlyingType(typeof(FlagsEnum));
+        _ = Enum.GetValuesAsUnderlyingType<FlagsEnum>().Length;
+#pragma warning restore NEEG010
+    }
+#endif
 }