$ git clone -n https://src.fedoraproject.org/rpms/thunderbird.git /var/lib/mock/f41-build-side-1-3125192-39488/root/chroot_tmpdir/scmroot/thunderbird
Cloning into '/var/lib/mock/f41-build-side-1-3125192-39488/root/chroot_tmpdir/scmroot/thunderbird'...
$ git fetch origin a276dc4459109f04817f24f1544f9416920fbdd6:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/thunderbird
 * [new ref]         a276dc4459109f04817f24f1544f9416920fbdd6 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a276dc4 +ExcludeArch: ppc64le  for all builds