graphics/digikam: update to 7.4.0, latest upstream

Release notes are at
https://www.digikam.org/news/2021-12-17-7.4.0_release_announcement/

DigiKam releases come with dozens of new features, too many
to recount in a commit message. I'll comment that the release
is an extra-annoying one because this time, the source
tarball has an upper-case-K which it didn't have previously.