fix(ci): add apt-get update before snapcraft install for arm64 build}
- Bump version from v2026.4.122 to v2026.4.123 - Add `sudo apt-get update` step before installing snapcraft in the arm64 CI workflow to prevent stale package index issues - Add changelog entry for v2026.4.123 documenting the arm64 snap build fix - Update build version references across README, artifacts, and changelog files