chore: enable Microsoft.Testing.Platform for internal tests

[mxschmitt]

Interestingly Command + C does not work aka. no way of aborting the test run and there is no visible live output when running

dotnet test -f net8.0 ./src/Playwright.Tests/Playwright.Tests.csproj --logger:"console;verbosity=detailed"

Looks related to TestingPlatformDotnetTestSupport when removing this and its using vstest it seems to work.

[nohwnd]

at the moment you will have better time moving to MTP, but instead of using dotnet test, you would be running the exe directly. (or dotnet exec on server, and probably dotnet run locally to ensure you re-build if there are changes).

Or you could update to net10 preview sdks where we are adding a new experience for dotnet test.