Bump MSTest.TestFramework in /FeatureFlags/FeatureFlags.FunctionalTests

Bumps [MSTest.TestFramework](https://github.com/microsoft/testfx) from 2.2.5 to 2.2.6.
- [Release notes](https://github.com/microsoft/testfx/releases)
- [Commits](microsoft/testfx@v2.2.5...v2.2.6)

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

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

FeatureFlags/FeatureFlags.FunctionalTests/FeatureFlags.FunctionalTests.csproj

@@ -10,7 +10,7 @@
     <PackageReference Include="Microsoft.Extensions.Configuration.AzureKeyVault" Version="3.1.18" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.11.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="2.2.6" />
-    <PackageReference Include="MSTest.TestFramework" Version="2.2.5" />
+    <PackageReference Include="MSTest.TestFramework" Version="2.2.6" />
     <PackageReference Include="coverlet.collector" Version="3.1.0">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>