Make RPIC deploy non-blocking while cluster is out of service

The Raspberry Pi cluster is temporarily out of service. Mark its deploy
step continue-on-error so its failure no longer skips the Gimli deploy
or fails the whole job. Revert once the cluster is back online.

.github/workflows/build-docker-images.yml

@@ -128,6 +128,10 @@ jobs:
           management-url: ${{ secrets.NETBIRD_URL }}
 
       - name: Deploy to RPIC-Cluster
+        # RPIC cluster is temporarily out of service. Don't let its failure
+        # block the Gimli deploy or fail the whole job. Remove this line once
+        # the cluster is back.
+        continue-on-error: true
         uses: appleboy/ssh-action@v1
         with:
           host: ${{ secrets.RPIC_HOST }}