$ git clone -n https://src.fedoraproject.org/rpms/thunderbird.git /var/lib/mock/f42-build-side-1-3580336-46819/root/chroot_tmpdir/scmroot/thunderbird
Cloning into '/var/lib/mock/f42-build-side-1-3580336-46819/root/chroot_tmpdir/scmroot/thunderbird'...
$ git fetch origin ac1df656bc288169c965d2cc6a879f91e6f25029:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/thunderbird
 * [new ref]         ac1df656bc288169c965d2cc6a879f91e6f25029 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ac1df65 Temporarily ExcludeArch aarch64 on f42, f43 due to gkrust link error