Bump MSTest.TestAdapter from 4.1.0 to 4.2.1

---
updated-dependencies:
- dependency-name: MSTest.TestAdapter
  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]

MyNumberNET_Test/MyNumberNET_Test.csproj

@@ -12,7 +12,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.4.0" />
-    <PackageReference Include="MSTest.TestAdapter" Version="4.1.0" />
+    <PackageReference Include="MSTest.TestAdapter" Version="4.2.1" />
     <PackageReference Include="MSTest.TestFramework" Version="4.2.1" />
     <PackageReference Include="xunit" Version="2.9.3" />
   </ItemGroup>