$ git clone -n https://src.fedoraproject.org/rpms/thunderbird.git /var/lib/mock/f39-build-2014168-45957/root/chroot_tmpdir/scmroot/thunderbird
Cloning into '/var/lib/mock/f39-build-2014168-45957/root/chroot_tmpdir/scmroot/thunderbird'...
$ git fetch origin 088a10bc67d9688c218a873f5c9c5d2b6df7af88:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/thunderbird
 * [new ref]         088a10bc67d9688c218a873f5c9c5d2b6df7af88 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 088a10b Update to 115.5.2