pgsql: Add retries for further investigation of 019_replslot_limit.pl f

Add retries for further investigation of 019_replslot_limit.pl failures.

Tom noticed evidence in the buildfarm suggesting the failures might just be
really slow process exits. To investigate further, instead of giving up after
seeing multiple walsender pids once, retry. For now continue to report test
failure if a retry succeeds.

See also commit afdeff10526 and fe0972ee5e6.

Per suggestion from Tom Lane.

Discussion: https://postgr.es/m/3042597.1648148740@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f28bf667f602f6ff36c219eb40c5f61de4440ae5

Modified Files
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src/test/recovery/t/019_replslot_limit.pl | 40 ++++++++++++++++++++++---------
1 file changed, 29 insertions(+), 11 deletions(-)