pgsql: Fix flag tests in src/test/modules/test_oat_hooks

Fix flag tests in src/test/modules/test_oat_hooks

In what must have been a copy'n paste mistake, all the flag tests use
the same flag rather than a different flag each. The bug is not
suprising, considering that it's dead code; add a minimal, testimonial
line to cover it.

This is all pretty inconsequential, because this is just example code,
but it had better be correct.

Discussion: https://postgr.es/m/20220712152059.fwli2majwgzdmh4r@alvherre.pgsql

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f16180216d0a6dcefd76fef4121227b63df46681

Modified Files
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src/test/modules/test_oat_hooks/expected/test_oat_hooks.out | 13 ++++++++++++-
src/test/modules/test_oat_hooks/sql/test_oat_hooks.sql | 5 ++++-
src/test/modules/test_oat_hooks/test_oat_hooks.c | 10 +++++-----
3 files changed, 21 insertions(+), 7 deletions(-)