Update MSTest to 3.9.0 (#46297)

---
updated-dependencies:
- dependency-name: MSTest
  dependency-version: 3.9.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

docs/core/testing/snippets/testcontext/csharp/project.csproj

@@ -8,7 +8,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="MSTest" Version="3.8.3" />
+    <PackageReference Include="MSTest" Version="3.9.0" />
   </ItemGroup>
 
 </Project>