MDEV-34721: Make debian/autobake-debs.sh change compat level when needed

[illuusio]

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• [x] The Jira issue number for this PR is: MDEV-34721

Description

Debian Deb Compat level version 12 brings more Systemd confort to Debian package installation handling. Althought it's not working correctly on certain Debian and Ubuntu version which MariaDB supports.

Commit add change to compat level to version 12 when it's should be working correctly.

Currently these distros that are changed:

• Debian Bullseye (11)
• Debian Bookwork (12)
• Debian Trixie (13)
• Debian Sid
• Ubuntu Lunar (23.04)
• Ubuntu Mantic (23.10)
• Ubuntu Noble (24.04)
• Ubuntu Oracular (24.10)

Release Notes

Bit tricky one as this changes compat level but should not be seen to user anyhow

How can this PR be tested?

Manually on docker one can pull repo and run AUTOBAKE_PREP_CONTROL_RULES_ONLY=1 debian/autobuild-debs.sh and see with git diff if changes have been made or not. One can also download debs from this Salsa-CI build to test with https://salsa.debian.org/illuusio/mariadb-server/-/commit/5efd075a00b80d916cf25f92b0bc433ef9cb4d46

and see if that build is all green.

Basing the PR against the correct MariaDB version

• [x] This is a bug fix, and the PR is based against the earliest maintained branch in which the bug can be reproduced.

PR quality check

• [x] I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
• [x] For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.