Also build PRs

.github/workflows/build.yml

@@ -4,6 +4,9 @@ on:
   push:
     branches:
       - master
+  pull_request:
+    branches:
+      - master
   schedule:
     - cron: '0 0 * * *'
 
@@ -36,6 +39,7 @@ jobs:
       - uses: actions/checkout@v2
 
       - uses: docker/login-action@v1
+        if: github.event_name != 'pull_request'
         with:
           registry: ghcr.io
           username: ${{ github.actor }}
@@ -50,6 +54,6 @@ jobs:
       - uses: docker/build-push-action@v2
         with:
           context: ${{ matrix.context }}
-          push: true
+          push: ${{ github.event_name != 'pull_request' }}
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}