$ git clone -n https://src.fedoraproject.org/rpms/fedora-appstream-metadata.git /var/lib/mock/f42-build-3275513-41321/root/chroot_tmpdir/scmroot/fedora-appstream-metadata
Cloning into '/var/lib/mock/f42-build-3275513-41321/root/chroot_tmpdir/scmroot/fedora-appstream-metadata'...
$ git fetch origin ec5889ba39601565a59a6f851d6a93a17f1c7c64:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/fedora-appstream-metadata
 * [new ref]         ec5889ba39601565a59a6f851d6a93a17f1c7c64 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ec5889b Update for F42 branching