Guix builds fail in pipeline on tags

Job "Guix-git-indent" fail on tags:

$ git checkout $CI_COMMIT_BRANCH
$ guix build -f guix.scm
updating checkout of '/builds/gnutls/guile'...
guix build: error: Git failure while fetching /builds/gnutls/guile: reference 'refs/remotes/origin/HEAD' not found

Ways to resolve:

1. Some build command change so it doesn't mess with git repository?

2. Don't run on tags