testing: add panic on any os.Exit call, not only zero code

[goto1134]

Fixes #61839

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Message from Ian Lance Taylor:

Patch Set 1:

(3 comments)

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This PR (HEAD: 4e4a9cf) has been imported to Gerrit for code review.

Please visit Gerrit at https://go-review.googlesource.com/c/go/+/517355.

Important tips:

• Don't comment on this PR. All discussion takes place in Gerrit.
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• To change your code in response to feedback:
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  • A new "patch set" will then appear in Gerrit.
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Message from Andrei Efanov:

Patch Set 1:

(3 comments)

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Message from Russ Cox:

Patch Set 2: Hold+1

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