Flowzone: Allow external contributions

Update the flowzone workflow to allow external PRs from forks

Change-type: patch
Signed-off-by: Florin Sarbu <florin@balena.io>

.github/workflows/flowzone.yml

@@ -6,9 +6,20 @@ on:
     branches:
       - "main"
       - "master"
+  # allow external contributions to use secrets within trusted code
+  pull_request_target:
+    types: [opened, synchronize, closed]
+    branches:
+      - "main"
+      - "master"
 
 jobs:
   flowzone:
     name: Flowzone
     uses: product-os/flowzone/.github/workflows/flowzone.yml@master
+    # prevent duplicate workflows and only allow one `pull_request` or `pull_request_target` for
+    # internal or external contributions respectively
+    if: |
+      (github.event.pull_request.head.repo.full_name == github.repository && github.event_name == 'pull_request') ||
+      (github.event.pull_request.head.repo.full_name != github.repository && github.event_name == 'pull_request_target')
     secrets: inherit