The labeler only listened for issues.opened, so it judged a title exactly
once. Reporters who omit the prefix are asked by the triage bot to add one,
and the title they then fix is never looked at again, leaving a genuine bug
report unlabelled until somebody notices it by hand.
It now also runs on issues.edited. Body only edits return immediately, so
the extra runs are limited to titles actually changing, and a bug label a
maintainer has already removed is not restored: on an edit the issue events
are checked for a previous removal first. The opened path is unchanged and
makes no additional API call.
The title pattern also required a delimiter after the bracket, so the
bracketed form the comment advertises, "[Bug] something is broken", never
matched unless it happened to be written "[Bug]: something is broken".
Both forms match now, while "[bug/perf]" keeps matching and titles that
merely mention the word, such as "[UI Bug]" or "fixed a typo", still do not.
