fix: flatpak

Author: drahnr

.concourse/tasks/flatpak.yml

@@ -20,6 +20,7 @@ run:
     flatpak-builder \
       --install \
       --user \
+      --force-clean \
       --default-branch=$FP_BRANCH \
       --state-dir=$FPB_WRKDIR/flatpak-builder \
       --repo=$FPB_WRKDIR/flatpak-repo \