Updating tests to use xUnit v3 and MTP

[Keboo]

No description provided.

[corvinsz]

I think this can easily be fixed with a little regex magic?
Replace:

await\s+Task\.Delay\s*\(\s*([^)]*?)\s*\)\s*;

With

await Task.Delay($1, TestContext.Current.CancellationToken);

And don't forget to check Use regular expressions

[Keboo]

Closing in favor of #3838