[9.20] chg: ci: Drop removed system tests from cross-version-config-tests
requested to merge backport-mnowak/remove-dialup-from-cross-version-config-tests-job-9.20 into bind-9.20
The cross-version-config-tests job fails when a system test is removed from the upcoming release. To avoid this, remove the system test also from the $BIND_BASELINE_VERSION.
See the failure mode at https://gitlab.isc.org/isc-projects/bind9/-/jobs/4668947.
Backport of MR !9413 (merged)