Fix fallback implementation for pg_atomic_test_set_flag().
The fallback implementation of pg_atomic_test_set_flag() that uses
atomic-exchange gives pg_atomic_exchange_u32_impl() an extra
argument. This issue has been present since the introduction of
the atomics API in commit
b64d92f1a5.
Reviewed-by: Andres Freund
Discussion: https://postgr.es/m/
20231114035439.GA1809032%40nathanxps13
Backpatch-through: 12