[clang][NFC] Add marking to CWG2947 test (#181832)
052f2f8cd17f3ff8bcb7b53a777a232d9ac36965 accidentally changed the status
of CWG2947 from "Clang 23" to "No", because the test was missing the
special comment that `make_cxx_dr_status` scripts consumes. This PR adds
the special comments and restores the original status of CWG2947.
