Bump the dotnet group (#43859)

Bumps the dotnet group in /docs/core/tutorials/snippets/library-with-visual-studio/csharp/StringLibraryTestNet8 with 2 updates: [MSTest.TestAdapter](https://github.com/microsoft/testfx) and [MSTest.TestFramework](https://github.com/microsoft/testfx).


Updates `MSTest.TestAdapter` from 3.6.3 to 3.6.4
- [Release notes](https://github.com/microsoft/testfx/releases)
- [Changelog](https://github.com/microsoft/testfx/blob/main/docs/Changelog.md)
- [Commits](microsoft/testfx@v3.6.3...v3.6.4)

Updates `MSTest.TestFramework` from 3.6.3 to 3.6.4
- [Release notes](https://github.com/microsoft/testfx/releases)
- [Changelog](https://github.com/microsoft/testfx/blob/main/docs/Changelog.md)
- [Commits](microsoft/testfx@v3.6.3...v3.6.4)

---
updated-dependencies:
- dependency-name: MSTest.TestAdapter
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: dotnet
- dependency-name: MSTest.TestFramework
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: dotnet
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

docs/core/tutorials/snippets/library-with-visual-studio/csharp/StringLibraryTestNet8/StringLibraryTest.csproj

@@ -11,8 +11,8 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
-    <PackageReference Include="MSTest.TestAdapter" Version="3.6.3" />
-    <PackageReference Include="MSTest.TestFramework" Version="3.6.3" />
+    <PackageReference Include="MSTest.TestAdapter" Version="3.6.4" />
+    <PackageReference Include="MSTest.TestFramework" Version="3.6.4" />
     <PackageReference Include="coverlet.collector" Version="6.0.2" />
   </ItemGroup>