$ git clone -n https://src.fedoraproject.org/rpms/thunderbird.git /var/lib/mock/f40-build-1209486-22540/root/chroot_tmpdir/scmroot/thunderbird
Cloning into '/var/lib/mock/f40-build-1209486-22540/root/chroot_tmpdir/scmroot/thunderbird'...
$ git fetch origin c9712f8c61d7bd7dcc9685d640bb2ddf8a1b5553:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/thunderbird
 * [new ref]         c9712f8c61d7bd7dcc9685d640bb2ddf8a1b5553 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c9712f8 Merge remote-tracking branch 'origin/rawhide' into f40