Race condition in server-crash testing

My pet dinosaur gaur just failed [1] in
src/test/recovery/t/022_crash_temp_files.pl, which does this:

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my $ret = PostgreSQL::Test::Utils::system_log('pg_ctl', 'kill', 'KILL', $pid);
is($ret, 0, 'killed process with KILL');

# Close psql session
$killme->finish;
$killme2->finish;

# Wait till server restarts
$node->poll_query_until('postgres', undef, '');
-----

It's hard to be totally sure, but I think what happened is that
gaur hit the in-hindsight-obvious race condition in this code:
we managed to execute a successful iteration of poll_query_until
before the postmaster had noticed its dead child and commenced
the restart.  The test lines after these are not prepared to see
failure-to-connect.

It's not obvious to me how to remove this race condition.
Thoughts?

            regards, tom lane

[1] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=gaur&dt=2022-04-03%2021%3A14%3A41