pgsql: Use correct DatumGet*() function in test_shm_mq_main().

Use correct DatumGet*() function in test_shm_mq_main().

This is purely cosmetic, as dsm_attach() interprets its argument as
a dsm_handle (i.e., an unsigned integer), but we might as well fix
it.

Oversight in commit 4db3744f1f.

Author: Jianghua Yang <yjhjstz@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAAZLFmRxkUD5jRs0W3K%3DUe4_ZS%2BRcAb0PCE1S0vVJBn3sWH2UQ%40mail.gmail.com
Backpatch-through: 13

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/e2f06282124b86a8ab7604c51de2dad749266fee

Modified Files
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src/test/modules/test_shm_mq/worker.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)