Fix build warnings that was annoying

Author: zlepper

Rebus.Diagnostics.Tests/Incoming/HandlerInvokerWrapperTests.cs

@@ -44,7 +44,7 @@ public async Task CreatesNewSubActivityIfThereIsAnActiveActivity()
         }
 
         [Test]
-        public async Task MarksActivityAsFailedIfHandlerThrows()
+        public void MarksActivityAsFailedIfHandlerThrows()
         {
             using var activity = new Activity("MyActivity");
 

Rebus.Diagnostics.Tests/Incoming/IncomingDiagnosticsStepTests.cs

@@ -331,7 +331,7 @@ private string RenderString(string message, object[] objs)
         /// <summary>
         ///     Formatter function that is invoked for each object value to be rendered into a string while interpolating log lines
         /// </summary>
-        private string FormatObject(object obj, string format)
+        private string FormatObject(object obj, string? format)
         {
             if (obj is string) return $@"""{obj}""";
             if (obj is IEnumerable)
@@ -345,7 +345,7 @@ private string FormatObject(object obj, string format)
             if (obj is DateTimeOffset) return ((DateTimeOffset) obj).ToString(format ?? "O");
             if (obj is IFormattable) return ((IFormattable) obj).ToString(format, CultureInfo.InvariantCulture);
             if (obj is IConvertible) return ((IConvertible) obj).ToString(CultureInfo.InvariantCulture);
-            return obj.ToString();
+            return obj.ToString()!;
         }
 
         #endregion

Rebus.Diagnostics.Tests/Outgoing/OutgoingDiagnosticsStepTests.cs

@@ -15,7 +15,7 @@ namespace Rebus.Diagnostics.Tests.Outgoing
     [TestFixture]
     public class OutgoingDiagnosticsStepTests : FixtureBase
     {
-        RebusTransactionScope? _scope;
+        RebusTransactionScope _scope = null!;
 
         [OneTimeSetUp]
         public static void ListenForRebus()