Update MSTest to 3.9.1

---
updated-dependencies:
- dependency-name: MSTest
  dependency-version: 3.9.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

docs/ai/tutorials/snippets/evaluate-safety/EvaluateResponseSafety.csproj

@@ -19,7 +19,7 @@
     <PackageReference Include="Microsoft.Extensions.Configuration" Version="9.0.5" />
     <PackageReference Include="Microsoft.Extensions.Configuration.UserSecrets" Version="9.0.5" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.0" />
-    <PackageReference Include="MSTest" Version="3.8.0" />
+    <PackageReference Include="MSTest" Version="3.9.1" />
   </ItemGroup>
 
   <ItemGroup>