$ git clone -n https://src.fedoraproject.org/rpms/grubby.git /var/lib/mock/f40-build-2236726-53519/root/chroot_tmpdir/scmroot/grubby
Cloning into '/var/lib/mock/f40-build-2236726-53519/root/chroot_tmpdir/scmroot/grubby'...
$ git fetch origin 893f94f4284445d5337ccd7c08aa265ef9d09f86:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/grubby
 * [new ref]         893f94f4284445d5337ccd7c08aa265ef9d09f86 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 893f94f Don't overwrite vars that start with GRUB_CMDLINE_LINUX