pgsql: Don't write to postgres's stdin in shmem startup failure test

Don't write to postgres's stdin in shmem startup failure test

The single-user test expects postgres to fail during startup, before
processing any queries. Sending the preceding test's queries can race
with that exit and make IPC::Run abort on a broken pipe. To fix, pass
empty input instead.

Author: Ayush Tiwari <ayushtiwari(dot)slg01(at)gmail(dot)com>
Reported-by: Alexander Lakhin <exclusion(at)gmail(dot)com>
Discussion: https://www.postgresql.org/message-id/e87c8fef-e254-441e-b889-bbcbd5afea7f@gmail.com
Backpatch-through: 19

Branch
------
REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/30ad431de3566252874fbf3c88897f8045122471

Modified Files
--------------
src/test/modules/test_shmem/t/001_late_shmem_alloc.pl | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)