Fix some warnings in the IDE

I turned on solution-wide analysis and these appeared in the error list.

.editorconfig

@@ -393,6 +393,7 @@ dotnet_diagnostic.IDE0090.severity = warning      # Use new(...)
 dotnet_diagnostic.IDE0220.severity = warning      # Add explicit cast
 dotnet_diagnostic.IDE0250.severity = warning      # Struct can be made 'readonly'
 dotnet_diagnostic.IDE0251.severity = suggestion   # Struct methods can be made 'readonly'
+dotnet_diagnostic.IDE0270.severity = suggestion   # Use coalesce expression
 dotnet_diagnostic.IDE1006.severity = warning      # Naming styles                                 Task Open()                                         Task OpenAsync()
 dotnet_diagnostic.IDE1006WithoutSuggestion.severity = suggestion
 
@@ -442,4 +443,5 @@ dotnet_diagnostic.CA1307.severity = suggestion    # Specify StringComparison
 # Disabling warning for C# files generated from xaml rules
 [artifacts/*/obj/Microsoft.VisualStudio.ProjectSystem.Managed/net8.0/*.cs]
 # CS0618: Type or member is obsolete
-dotnet_diagnostic.CS0618.severity = silent
+dotnet_diagnostic.CS0618.severity = silent
+

tests/Common/ThrowingTraceListener.cs

@@ -1,7 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements. The .NET Foundation licenses this file to you under the MIT license. See the LICENSE.md file in the project root for more information.
 
 using System.Diagnostics;
+#if !NET8_0_OR_GREATER
 using System.Runtime.Serialization;
+#endif
 
 namespace Microsoft.VisualStudio.Diagnostics
 {

tests/Microsoft.VisualStudio.ProjectSystem.Managed.VS.UnitTests/ProjectSystem/VS/ComponentVerificationTests.cs

@@ -21,8 +21,8 @@ public void ImportsMustFilterBasedOnCapabilities(Type type)
 
             foreach ((ImportDefinitionBinding import, IReadOnlyList<ExportDefinitionBinding> exports) in part.SatisfyingExports)
             {
-                var importingProperty = import.ImportingMember as PropertyInfo;
-                if (importingProperty is null)  // We don't verify ImportingConstructor, only check properties.
+                // Only check properties. We don't verify ImportingConstructor.
+                if (import.ImportingMember is not PropertyInfo importingProperty)
                     return;
 
                 Type memberType = importingProperty.PropertyType;