$ git clone -n https://src.fedoraproject.org/rpms/rubygem-mercenary.git /var/lib/mock/f45-build-35035-693/root/chroot_tmpdir/scmroot/rubygem-mercenary
Cloning into '/var/lib/mock/f45-build-35035-693/root/chroot_tmpdir/scmroot/rubygem-mercenary'...
$ git fetch origin 40e810a2fa90e5f9b8d6c9e7292bd28aa678798a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-mercenary
 * [new ref]         40e810a2fa90e5f9b8d6c9e7292bd28aa678798a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 40e810a Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild