Bump Microsoft.NET.Test.Sdk in /FeatureFlags/FeatureFlags.Tests

Bumps [Microsoft.NET.Test.Sdk](https://github.com/microsoft/vstest) from 16.8.3 to 16.9.1.
- [Release notes](https://github.com/microsoft/vstest/releases)
- [Commits](microsoft/vstest@v16.8.3...v16.9.1)

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

FeatureFlags/FeatureFlags.Tests/FeatureFlags.Tests.csproj

@@ -31,7 +31,7 @@
     <PackageReference Include="Microsoft.Extensions.Configuration" Version="5.0.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="5.0.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration.UserSecrets" Version="5.0.0" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.8.3" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.9.1" />
     <PackageReference Include="Moq" Version="4.16.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="2.1.2" />
     <PackageReference Include="MSTest.TestFramework" Version="2.1.2" />