pgsql: Stabilize xid_wraparound/t/002_limits.pl test.

Stabilize xid_wraparound/t/002_limits.pl test.

Not many buildfarm members run this test, since it's gated behind
PG_TEST_EXTRA=xid_wraparound, but of those that do, the slower ones
not infrequently fail. The reason seems to be that the test expects
an INSERT command to either succeed or fail, but there's a window
where it can succeed while issuing a warning about impending
wraparound. poll_query_until treats nonempty stderr as a failure,
so it loops an extra time until the INSERT succeeds with no warning.
There seems no reason to treat this behavior as wrong, so adjust
the test to accept it.

Reported-by: Alexander Lakhin <exclusion(at)gmail(dot)com>
Diagnosed-by: Alexander Lakhin <exclusion(at)gmail(dot)com>
Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/7a68bee2-91bd-481d-be44-160e6beebc83@gmail.com
Backpatch-through: 17

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e073b64d33215d4bfded1366549b96580a402c06

Modified Files
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src/test/modules/xid_wraparound/t/002_limits.pl | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)