Fix github actions for pull requests (#271)

.github/workflows/docker.yml

@@ -5,6 +5,9 @@ on:
     branches:
       - '*'
   pull_request:
+  # Enabling this has some security implications.  For now we'll leave it off.
+  #pull_request_target:
+  #  types: [labeled]
   schedule:
     - cron: '42 06 * * sat' # Run every Saturday at 06:42 UTC
 
@@ -42,7 +45,7 @@ jobs:
       uses: docker/build-push-action@v5
       with:
         context: .
-        push: ${{ github.event_name != 'schedule' }}
+        push: ${{ github.event_name == 'push' || ( github.event_name == 'pull_request_target' && contains(github.event.pull_request.labels.*.name, 'push to docker'))}}
         build-args: |
           CFLAGS=
           NCPU=4