Mixer settings are saved in file but score not dirty when settings changes
Steps to reproduce:
1. Open a score
2. Change the Mixer settings
Expected behavior: Score should appear with an asterisk in the window tab title.
Actual behavior: Score is not marked with asterisk.
Discussion: This is bordering on critical priority since MuseScore won't prompt to save if the user closes the score after changing the Mixer settings. The changes are lost.
GIT commit: 7769088
Report opened as a result of closing the following report: #4621: Relative tempo is saved in file but score not dirty when tempo changes