chg: ci: Adjust allow_failure in cross-version-config tests

The failures caused by #6007 are longer happening.

However, in the mean time, other tests have begun to fail due to https://gitlab.isc.org/isc-projects/bind9/-/merge_requests/12163/diffs?commit_id=9771df0aca5ce399ad0535f656c403a58d674606

Merge branch 'nicki/revert-allow-failure-after-9.21.23' into 'main'

See merge request isc-projects/bind9!12264