The test output varies when debug_discard_caches is enabled,
because that causes extra executions of recomputeNamespacePath.
Maybe putting a hook in that was a bad idea, but as a stopgap,
just turn off debug_discard_caches in this test.
Per buildfarm (now that we have debug_discard_caches coverage
again). Back-patch to v15 where this module was added.
Discussion: https://postgr.es/m/2267406.1668804934@sss.pgh.pa.us
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