Hardening the CI in relation to PRs

.github/workflows/build.yml

@@ -1,6 +1,8 @@
 name: Build
 on:
-  [push]
+  push:
+  pull_request_target:
+    types: [labeled]
 jobs:
   build:
     name: Build and Test
@@ -31,4 +33,4 @@ jobs:
         with:
           prerelease: true
           token: ${{ secrets.CRYPTOBOT_RELEASE_TOKEN }}
-          generate_release_notes: true
+          generate_release_notes: true