Detect SystemExit in tests and convert it to an error

What does this MR do and why?

Detect SystemExit in tests and convert it to an error

Because if we let it fall through, it'll stop the tests early. Make sure it's handled.

We do 2 things here:

• Make sure we catch all potential SystemExit so we never cut the tests early
• This also reverts !77955 (merged) in case we do need exit right there.

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MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

See #350060 (closed)