Rethink blocking annotations in detach-partition-concurrently-[34].

Rethink blocking annotations in detach-partition-concurrently-[34].

In 741d7f104, I tried to make the reports from canceled steps come out
after the pg_cancel_backend() steps, since that was the most common
ordering before.  However, that doesn't ensure that a canceled step
doesn't report even later, as shown in a recent failure on buildfarm
member idiacanthus.  Rather than complicating things even more with
additional annotations, let's just force the cancel's effect to be
reported first.  It's not *that* unnatural-looking.

Back-patch to v14 where these test cases appeared.

Report: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=idiacanthus&dt=2021-07-02%2001%3A40%3A04