$ git clone -n https://src.fedoraproject.org/rpms/plasma-activities.git /var/lib/mock/f42-build-side-1-3497621-45961/root/chroot_tmpdir/scmroot/plasma-activities
Cloning into '/var/lib/mock/f42-build-side-1-3497621-45961/root/chroot_tmpdir/scmroot/plasma-activities'...
$ git fetch origin 66478916758a9bce7fce73c39abf03afd0450ef5:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/plasma-activities
 * [new ref]         66478916758a9bce7fce73c39abf03afd0450ef5 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 6647891 6.3.4