pgsql: Remove race condition in 022_crash_temp_files.pl test.

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

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/9a7229948c70945ca6ef0b36adfe61b74f4fdaf5

Modified Files
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src/test/recovery/t/022_crash_temp_files.pl | 34 ++++++++++++++++++++++++-----
1 file changed, 29 insertions(+), 5 deletions(-)