Fixes for branches of interest in frozen tier 0 tests

This MR does two things

1. Fixes for !67801 (merged), which was checking for matches in the wrong place (you can read more here !67845 (comment 7464456)). I also renamed some variables to try and make the logic in this code more clear
2. Catches ERROR messages in logs and fails CI tests if they are present. The current behaviour fails on WARNING but not ERROR, which is unintuitive

@dguest @bdong @tstreble @tadej