Prepare MariaDB Server 1:11.4.2-1 for upload to Debian

See commits for details. Focus review only on the commits done on this Debian packaging branch (i.e. don't review commits that have already been merged upstream, we are not re-reviewing them here).

Test builds and test suite on multiple architectures pass at https://launchpad.net/~mysql-ubuntu/+archive/ubuntu/mariadb/+builds?build_text=&build_state=all.

Regarding CI failures, please compare to existing failures at https://salsa.debian.org/mariadb-team/mariadb-server/-/pipelines which appeared due to updates in dependencies starting from June 1st.