configure dependabot to keep base image & github-actions up-to-date
https://github.com/fphammerle/docker-onion-service/commit/16856af330263d1331895212ae2e6927a35159a4
https://github.com/fphammerle/ical2vdir/commit/76d3b61c128fe1cad322e52d5877cc919a533ac4