Remove race condition in 022_crash_temp_files.pl test.
It's possible for the query that "waits for restart" to complete a
successful iteration before the postmaster has noticed its SIGKILL'd
child and begun the restart cycle. (This is a bit hard to believe
perhaps, but it's been seen at least twice in the buildfarm, mainly
on ancient platforms that likely have quirky schedulers.)
To provide a more secure interlock, wait for the other session
we're using to report that it's been forcibly shut down.
Patch by me, based on a suggestion from Andres Freund.
Back-patch to v14 where this test case came in.
Discussion: https://postgr.es/m/
1801850.
1649047827@sss.pgh.pa.us