Bump System.Reactive.PlatformServices from 5.0.0 to 6.0.0

Bumps [System.Reactive.PlatformServices](https://github.com/dotnet/reactive) from 5.0.0 to 6.0.0.
- [Release notes](https://github.com/dotnet/reactive/releases)
- [Commits](https://github.com/dotnet/reactive/commits)

---
updated-dependencies:
- dependency-name: System.Reactive.PlatformServices
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

AspNetCoreAnalyzers.Tests/AspNetCoreAnalyzers.Tests.csproj

@@ -31,6 +31,6 @@
     <PackageReference Include="NUnit3TestAdapter" Version="4.4.2" PrivateAssets="all" />
     <PackageReference Include="ReflectionAnalyzers" Version="0.3.1" PrivateAssets="all" />
     <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.435" PrivateAssets="all" />
-    <PackageReference Include="System.Reactive.PlatformServices" Version="5.0.0" />
+    <PackageReference Include="System.Reactive.PlatformServices" Version="6.0.0" />
   </ItemGroup>
 </Project>