Disable recently added CIC/RI isolation tests

Disable recently added CIC/RI isolation tests

We have tried to stabilize them several times already, but they are very
flaky -- apparently there's some intrinsic instability that's hard to
solve with the isolationtester framework.  They are very noisy in CI
runs (whereas buildfarm has not registered any such failures).  They may
need to be rewritten completely.  In the meantime just comment them out
in Makefile/meson.build, leaving the spec files around.

Per complaint from Andres Freund.

Discussion: https://postgr.es/m/202512112014.icpomgc37zx4@alvherre.pgsql