exclude manual deploy-commit-to-staging from running on PR merge (#558)

.gitlab-ci.yml

@@ -209,6 +209,8 @@ deploy-commit-to-staging:
   <<:                     *deploy
   environment:
     name:                 parity-stg
+  rules:
+    - if: '$CI_COMMIT_BRANCH =~ /^[0-9]+/'
       when: manual
 
 # Automatically deploy `master` branch or tag like `v1.0` to staging