snap: update gnome-boxes to 50.0

[Copilot]

Pull Request Template

Description

Updates the snap to the latest upstream GNOME Boxes release. This keeps the packaged app aligned with current upstream while preserving the existing base and packaging structure.

• Upstream version

  • Bump the gnome-boxes part from 47.0 to 50.0
  • Keep version derivation unchanged via upstream tags

• Auto-update guard

  • Raise the update ceiling from < 48.0 to < 51.0 so automated refreshes can continue within the current supported range

gnome-boxes:
  source-tag: '50.0'
# ext:updatesnap
#   version-format:
#     lower-than: 51.0

Type of change

Please check only the options that are relevant.

• General Maintenance
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

YAML structure was validated after the update to confirm the snap metadata still parses with the new version values.

Test Configuration:

• OS (please include version): GitHub Actions runner environment
• Any other relevant environment information: local snapcraft CLI not available in this sandbox

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have checked my code and corrected any misspellings

[3v1n0]

I would rebase this also on #29

[3v1n0]

Ok, this needed some love (download was broken) and I had handled some changes myself in #29, but it's good to go now.