Issue with emacs 29

[Jonas Damm]

Hi,
I am using Emacs 29 and org-babel to create music sheets with lilypond.
For some reason the fontification is not working anymore:

[2. text/x-org]
#+begin_src lilypond

  \relative c' {
    c d e f g
    }

#+end_src

This gives an fontification error as soon as I enter the "{" (the same
goes for "{}[]").

I submitted this issue to the emacs bug mailing list. They gave me the
following advice:

Thank you!

Ihor Radchenko <yantar92@posteo.net> writes:

> This is a problem with lilypond:
>
> Debugger entered--Lisp error: (void-variable font-lock-reference-face)
>   (eval font-lock-reference-face t)
>   (#f(compiled-function (highlight) "Apply HIGHLIGHT following a
> match.\nHIGHLIGHT should be of the form MATCH-HIGHLIGHT, see
> `font-lock-keywords'." #<bytecode -0xf53eae0ec5f928c>) (0
> font-lock-reference-face t))
>   (font-lock-fontify-keywords-region 1 42 nil)
>   (font-lock-default-fontify-region 1 42 nil)
>   (font-lock-fontify-region 1 42)
>   (#f(compiled-function (beg end) #<bytecode -0x19f31ec42bd98447>) 1
> 42)
>   (font-lock-ensure)
>
> `font-lock-reference-face' is an obsolete variable that has been
> removed
> in Emacs 29.
>
> Please report this issue to Lilypond developers. See
> https://lilypond.org/bug-reports.html