$ git clone -n https://src.fedoraproject.org/rpms/mock.git /var/lib/mock/f39-build-1573625-37809/root/chroot_tmpdir/scmroot/mock
Cloning into '/var/lib/mock/f39-build-1573625-37809/root/chroot_tmpdir/scmroot/mock'...
$ git fetch origin 875b5f31ceac943c453ee0c4a8d8f1c53edbaed7:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mock
 * [new ref]         875b5f31ceac943c453ee0c4a8d8f1c53edbaed7 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 875b5f3 Update mock to 5.2-1