$ git clone -n https://src.fedoraproject.org/rpms/thunderbird.git /var/lib/mock/f42-build-3300822-41426/root/chroot_tmpdir/scmroot/thunderbird
Cloning into '/var/lib/mock/f42-build-3300822-41426/root/chroot_tmpdir/scmroot/thunderbird'...
$ git fetch origin 0c5cfad5ef0e5c12e820bacea7a2e4e09bf97579:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/thunderbird
 * [new ref]         0c5cfad5ef0e5c12e820bacea7a2e4e09bf97579 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0c5cfad Update to 128.8.0