Bump xunit.runner.visualstudio from 2.5.5 to 2.5.6 in /src

Bumps [xunit.runner.visualstudio](https://github.com/xunit/visualstudio.xunit) from 2.5.5 to 2.5.6.
- [Release notes](https://github.com/xunit/visualstudio.xunit/releases)
- [Commits](xunit/visualstudio.xunit@2.5.5...2.5.6)

---
updated-dependencies:
- dependency-name: xunit.runner.visualstudio
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

src/Tests/Tests.csproj

@@ -9,7 +9,7 @@
     <PackageReference Include="Xunit" Version="2.6.3" />
     <PackageReference Include="Verify.Xunit" Version="22.8.0" />
     <PackageReference Include="Verify.DiffPlex" Version="2.3.0" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.5.5" PrivateAssets="all" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.5.6" PrivateAssets="all" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
     <ProjectReference Include="..\SampleGenerator\SampleGenerator.csproj" />
     <ProjectReference Include="..\Verify.SourceGenerators\Verify.SourceGenerators.csproj" />