$ git clone -n https://src.fedoraproject.org/rpms/gap-pkg-json.git /var/lib/mock/f38-build-side-42-init-devel-907743-28633/root/chroot_tmpdir/scmroot/gap-pkg-json
Cloning into '/var/lib/mock/f38-build-side-42-init-devel-907743-28633/root/chroot_tmpdir/scmroot/gap-pkg-json'...
$ git fetch origin 39f010dc96ca3499b076a18456a650cb885fb874:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gap-pkg-json
 * [new ref]         39f010dc96ca3499b076a18456a650cb885fb874 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 39f010d Use the %gap_arches macro.