$ git clone -n https://src.fedoraproject.org/rpms/boom-boot.git /var/lib/mock/f41-build-side-1-2749782-31006/root/chroot_tmpdir/scmroot/boom-boot
Cloning into '/var/lib/mock/f41-build-side-1-2749782-31006/root/chroot_tmpdir/scmroot/boom-boot'...
$ git fetch origin 5db3c24c0f42c22b88ed2f3ffe0006abf8d640b5:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/boom-boot
 * [new ref]         5db3c24c0f42c22b88ed2f3ffe0006abf8d640b5 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 5db3c24 Update boom-boot to upstream version 1.6.5