pgsql: tests: Cope with WARNINGs during failed CREATE DB on windows

tests: Cope with WARNINGs during failed CREATE DB on windows

The test added in 93bc3d75d8e sometimes fails on windows, due to warnings like
WARNING:  some useless files may be left behind in old database directory "base/16514"

The reason for that is createdb_failure_callback() does not ensure that there
are no open file descriptors for files in the partially created,
to-be-dropped, database. We do take care in dropdb(), but that involves
waiting for checkpoints and a ProcSignalBarrier, which we probably don't want
to do in an error callback.  This should probably be fixed one day, but for
now 001_aio.pl needs to cope.

Per buildfarm animals fairywren and drongo.

Discussion: https://postgr.es/m/uc62i6vi5gd4bi6wtjj5poadqxolgy55e7ihkmf3mthjegb6zl@zqo7xez7sc2r

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/43dca8a11624d02dde2b4bd348d77b7045c0dfbc

Modified Files
--------------
src/test/modules/test_aio/t/001_aio.pl | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)