scummvm: update to 2.9.1

[cmitu]

It's mostly a maintenance release, but some new features:

• AGI:
  • Added support for early version of Christmas Card 1986 with advertisements for Tandy hardware.
• AGS:
  • Added official support for Old Skies and Rosewater

Full changelog - https://downloads.scummvm.org/frs/scummvm/2.9.1/ReleaseNotes.html