ci: use Node 16 in the release workflow

Merge pull request #24 from kffl/fix/undefined-index-scheme

fix: `undefined index: scheme` error

Merge pull request #21 from kffl/deps/nc25

deps: declare support for Nextcloud 25

Merge pull request #14 from kffl/feat/calendar-object-deleted-event

feat: add `CalendarObjectDeleted` and `CalendarObjectMovedToTrash` events

chore: bump app version

Merge pull request #8 from kffl/deps/nc24

deps: declare support for Nextcloud 24

chore: bump app version

ci: specify php version in release workflow