pgsql: Try to stabilize the reloptions test.

Try to stabilize the reloptions test.

Where we test vacuum_truncate's effects, sometimes this is failing to
truncate as expected on the build farm.  That could be explained by page
skipping, so disable it explicitly, with the theory that commit fe246d1c
didn't go far enough.

Back-patch to 12, where the vacuum_truncate tests were added.

Discussion: https://postgr.es/m/CA%2BhUKGLT2UL5_JhmBzUgkdyKfc%3D5J-gJSQJLysMs4rqLUKLAzw%40mail.gmail.com

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/bef165059268ad8b48b9163c4f62999f203b7782

Modified Files
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src/test/regress/expected/reloptions.out | 4 ++--
src/test/regress/sql/reloptions.sql      | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)