Bump CommunityToolkit.Diagnostics from 8.4.0 to 8.4.2

---
updated-dependencies:
- dependency-name: CommunityToolkit.Diagnostics
  dependency-version: 8.4.2
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

ThScoreFileConverter.Core/ThScoreFileConverter.Core.csproj

@@ -15,7 +15,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="CommunityToolkit.Diagnostics" Version="8.4.0" />
+    <PackageReference Include="CommunityToolkit.Diagnostics" Version="8.4.2" />
     <PackageReference Include="IDisposableAnalyzers" Version="4.0.8">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>