$ git clone -n https://src.fedoraproject.org/rpms/mock.git /var/lib/mock/f39-build-2265536-54601/root/chroot_tmpdir/scmroot/mock
Cloning into '/var/lib/mock/f39-build-2265536-54601/root/chroot_tmpdir/scmroot/mock'...
$ git fetch origin 99a5857822151dfe85c35f5168d27126fe0d3395:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mock
 * [new ref]         99a5857822151dfe85c35f5168d27126fe0d3395 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 99a5857 Update mock to 5.4-1