games/scummvm: Update to 2026.1.0

• Disable the newly introduced Musepack support for now, because it's hardly used by any engine at the moment.

• Complete the switch to the preferred DISTVERSION that was overlooked in 0a08a3270bad while I'm here.

• The version numbering scheme has been changed to YEAR.RELEASE.PATCH.

Changelog:

https://downloads.scummvm.org/frs/scummvm/2026.1.0/ReleaseNotes.html

MFH: No (feature release)