feat: only publish pkgs when we're in staging branches (#556)

See https://github.com/ooni/probe/issues/1506#issuecomment-949664779

.github/workflows/oohelperd.yml

@@ -1,9 +1,10 @@
-# oohelperd builds oohelperd for Linux
+# oohelperd builds and publishes oohelperd for Linux
 name: oohelperd
 on:
   push:
     branches:
       - "release/**"
+      - "oohelperd-staging"
 
 jobs:
   build_amd64:
@@ -31,6 +32,7 @@ jobs:
           dpkg-buildpackage -us -uc -b
 
       - name: upload package
+        if: github.ref == 'refs/heads/oohelperd-staging'
         run: |
           curl -fsSLO https://raw.githubusercontent.com/ooni/sysadmin/master/tools/debops-ci
           chmod +x debops-ci