workflows/backport: only trigger on backport labels

The backport job was previously triggered on any label activity, i.e.
when the backport label was already set and a new label added, the
backport would have been triggered again.

That's because github.event_name is actually "pull_request_target" in
this case, not "closed" or "labeled" (the event's types). Thus, this
part of the condition was always true.

This also means that the second part, the startsWith, was never
evaluated. It had its arguments flipped and would have always been
false.

This was introduced in #126825, but has never really worked as intended.

Resolves #199556

0 files changed, 0 insertions, 0 deletions