Semantic snippets test flaw

[DoctorKrolic]

Semantic snippets tests, which verify, that a snippet is absent in the given context, don't actually verify anything. As shown in #73908, a test, where foreach is clearly valid (a test above verifies that), doesn't fail in CI

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.