Bar_number_engraver: fix order dependence
Do not depend on Repeat_acknowledge_engraver::process_music () running before Bar_number_engraver::process_music ().
The 17.0 major release is coming on May 16, 2024! This version brings many exciting improvements to GitLab, but also removes some deprecated features. We are introducing three breaking change windows during which we expect breaking changes to be deployed to GitLab.com. You can read more about it on our blogpost. The first breaking change window begins 2024-04-22 09:00UTC and ends 2024-04-24 22:00UTC.
Do not depend on Repeat_acknowledge_engraver::process_music () running before Bar_number_engraver::process_music ().