bootstrap: --fail-fast doesn't work anymore

[jyn514]

fail_fast is broken because anything calling try_run will panic immediately instead of waiting for all other steps to finish running.

@GuillaumeGomez do you have time to follow up here?

Originally posted by @jyn514 in #112962 (comment)

[GuillaumeGomez]

Sure.

[hameerabbasi]

Removing I-prioritize since this is already being worked on/in review.

@rustbot label -I-prioritize