lilypond: update to 2.23.9

[newbluemoon]

Testing the changes

• I tested the changes in this PR: YES

Finally getting rid of guile1.8! :)

Local build testing

• I built this PR locally for my native architecture, (x86_64, x86_64-musl, i686)
• I built this PR locally for these architectures (if supported. mark crossbuilds):
  • armv7l-musl

[newbluemoon]

All checks succeed locally. No clue why they sometimes fail with CI.

[newbluemoon]

Re-ran all checks, they succeed locally.

[newbluemoon]

All checks pass locally.

[paper42]

All checks pass locally.

Then please add make_check=ci-skip # reason

[newbluemoon]

@paper42 Done :)

[paper42]

we should add a notice near the top of lilypond and lilypond-doc that they should be kept in sync like it's done in vala and valadoc

[newbluemoon]

Done.