pgsql: Make after-startup shmem failure test reliable

Make after-startup shmem failure test reliable

The test expects a 128 kB request to exceed the shared memory available after
startup. Huge pages can round up the main shared memory segment enough for
that request to succeed, defeating the test.

Disable huge pages for the allocation-failure phase so that it exercises the
intended error path independently of shared memory segment rounding.

Author: Ayush Tiwari <ayushtiwari(dot)slg01(at)gmail(dot)com>
Reported-by: Andres Freund <andres(at)anarazel(dot)de>
Discussion: https://postgr.es/m/rpkhzrrmo7qiz7rr3qlufksb2oci33wcg3ao75le7dqindgoif@6yozkjwb6bdf
Backpatch-through: 19

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/61e64cb19a08c23dca1df46f1ae09df514059fc6

Modified Files
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src/test/modules/test_shmem/t/001_late_shmem_alloc.pl | 3 +++
1 file changed, 3 insertions(+)