fix: grow music inventory dynamically

[PierreSchwang]

Overview

Fixes #4567

Description

not tested, should work (i did test the math part though)

### Submitter Checklist
- [x] Make sure you are opening from a topic branch (**/feature/fix/docs/ branch** (right side)) and not your main branch.
- [x] Ensure that the pull request title represents the desired changelog entry.
- [x] New public fields and methods are annotated with `@since TODO`.
- [x] I read and followed the [contribution guidelines](https://github.com/IntellectualSites/.github/blob/main/CONTRIBUTING.md).

[SirYwell]

Looks good. If we update to Java 21, we can also use Math.ceilDiv there