deps: Bump MSTest from 4.1.0 to 4.2.1

---
updated-dependencies:
- dependency-name: MSTest
  dependency-version: 4.2.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

Directory.Packages.props

@@ -10,7 +10,7 @@
     <PackageVersion Include="IndexRange" Version="1.1.0" />
     <PackageVersion Include="Nullable" Version="1.3.1" />
     <!-- Testing -->
-    <PackageVersion Include="MSTest" Version="4.1.0" />
+    <PackageVersion Include="MSTest" Version="4.2.1" />
     <PackageVersion Include="coverlet.collector" Version="6.0.4" />
     <PackageVersion Include="Verify.MSTest" Version="31.12.5" />
   </ItemGroup>