$ git clone -n https://src.fedoraproject.org/rpms/rubygem-rspec-core.git /var/lib/mock/f38-build-side-42-init-devel-928676-28746/root/chroot_tmpdir/scmroot/rubygem-rspec-core
Cloning into '/var/lib/mock/f38-build-side-42-init-devel-928676-28746/root/chroot_tmpdir/scmroot/rubygem-rspec-core'...
$ git fetch origin c90c3940f344f18bcb75c37e58071e2ac85b5715:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-rspec-core
 * [new ref]         c90c3940f344f18bcb75c37e58071e2ac85b5715 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c90c394 3.12.1