pgsql: Fix 003_check_guc.pl when loading modules with custom GUCs

Fix 003_check_guc.pl when loading modules with custom GUCs

The test missed that custom GUCs need to be ignored from the list of
parameters that can exist in postgresql.conf.sample.  This caused the
test to fail on a server where such a module is loaded, when using
EXTRA_INSTALL and TEMP_CONFIG, for instance.

Author: Anton A. Melnikov
Discussion: https://postgr.es/m/fc5509ce-5144-4dac-8d13-21793da44fc5@postgrespro.ru
Backpatch-through: 15

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/2001aab86099e17dd4ea8dce362e225d50c26493

Modified Files
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src/test/modules/test_misc/t/003_check_guc.pl | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)