Update mstest monorepo to 4.2.1

Author: renovate[bot]

src/algorithm_exercises_csharp_test/algorithm_exercises_csharp_test.csproj

@@ -38,8 +38,8 @@
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
-    <PackageReference Include="MSTest.TestAdapter" Version="4.1.0" />
-    <PackageReference Include="MSTest.TestFramework" Version="4.1.0" />
+    <PackageReference Include="MSTest.TestAdapter" Version="4.2.1" />
+    <PackageReference Include="MSTest.TestFramework" Version="4.2.1" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.4" />
     <PackageReference Include="ReportGenerator" Version="5.5.4" />
   </ItemGroup>