Run dev release only if merged and labeled to build.

.github/workflows/release-dev.yaml

@@ -6,7 +6,7 @@
 
 name: release-dev
 on:
-  push:
+  pull_request:
     paths-ignore:
       - '.github/**'
       - '*.md'
@@ -16,7 +16,8 @@ on:
       - 'licenses/**'
       - 'tools/**'
     branches:
-      - dev      
+      - dev 
+    types: [closed]
   workflow_dispatch:
 
 env:
@@ -25,6 +26,7 @@ env:
 jobs:
   launch-dev-release:
       runs-on: ubuntu-20.04
+      if: github.event.pull_request.merged == 'true' && github.event.label.name == 'build'
       steps:
         - uses: actions/checkout@v2
           name: checkout