release-it: resolve "No names found, cannot describe anything" error

The release.sh script of the release-it image uses git describe --tags --abbrev=0 to parse all commits since the previous version. However, if the repo doesn't yet contain any tags this fails with the No names found, cannot describe anything error message. We need to fix this obviously.

This initially came to light in https://gitlab.developers.cam.ac.uk/uis/devops/gsuite/preferences-webapp/-/merge_requests/30