$ git clone -n https://src.fedoraproject.org/rpms/mailcommon.git /var/lib/mock/f40-build-762352-121982/root/chroot_tmpdir/scmroot/mailcommon
Cloning into '/var/lib/mock/f40-build-762352-121982/root/chroot_tmpdir/scmroot/mailcommon'...
$ git fetch origin 514655d759e5db6687f0e04621601dbbc5b4b66b:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mailcommon
 * [new ref]         514655d759e5db6687f0e04621601dbbc5b4b66b -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 514655d Updated -devel requires