Make Debian 12 "bookworm" the base image

When a new Debian stable image is released, it is posed to become our next CI base image. This is a good time to clean up accumulated workarounds from the current base image and BIND 9 CI. Debian 12 "bookworm" is expected to stabilize in mid-2023.

Images

Drop custom Unbound installation in favor of the unbound Debian package (https://gitlab.isc.org/isc-projects/images/-/merge_requests/222#note_354221)
~~Drop an upstream patch that prevents PyLint from reporting "no-member" errors for scripts using dnspython~~
Drop custom cmocka build if the distributed version is older than 1.1.3 (it is for all current Debian versions)
Drop ABI_CHECK - with BIND 9.11 EOL, we don't need those tools anymore
Bump reference BIND 9 for respdiff as BIND 9.11 likely won't build with GCC 12

BIND 9

Bring your own issues

Edited Sep 04, 2023 by Michal Nowak

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