aux-build `tests/crashes` tests don't seem to work

[BoxyUwU]

cc @jieyouxu

Is it possible to write a tests/crashes test with aux-build? @camelid tried in #131081 but tidy complains that crashes/auxiliary/aux123456.rs doesnt have a known-bug annotation/

[matthiaskrgr]

Ah yes, right now it simply checks every single file as I didn't have aux tests in mind 😅

Guess we can just ignore everything in crashes/auxiliary when checking for the bug number..?

[jieyouxu]

Probably a path suffix match, aux build logic expects aux file to be under an auxiliary/ folder.