Bump MSTest.TestFramework from 3.4.0 to 3.4.3 in /src.csharp (#28)

Bumps [MSTest.TestFramework](https://github.com/microsoft/testfx) from 3.4.0 to 3.4.3.
- [Release notes](https://github.com/microsoft/testfx/releases)
- [Changelog](https://github.com/microsoft/testfx/blob/main/docs/Changelog.md)
- [Commits](microsoft/testfx@v3.4.0...v3.4.3)

---
updated-dependencies:
- dependency-name: MSTest.TestFramework
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

src.csharp/AlphaTab.Test/AlphaTab.Test.csproj

@@ -13,7 +13,7 @@
     <ItemGroup>
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
         <PackageReference Include="MSTest.TestAdapter" Version="3.4.0" />
-        <PackageReference Include="MSTest.TestFramework" Version="3.4.0" />
+        <PackageReference Include="MSTest.TestFramework" Version="3.4.3" />
     </ItemGroup>
 
     <ItemGroup>