CI: build docker on pull request as well

Author: JulianFP

.github/workflows/docker.yml

@@ -5,6 +5,9 @@ on:
       - main
     tags:
       - "v*"
+  pull_request:
+    branches:
+      - main
 
 jobs:
   docker-build:
@@ -30,6 +33,6 @@ jobs:
       - uses: docker/build-push-action@v6
         with:
           context: .
-          push: true
+          push: ${{ github.event_name != 'pull_request' }}
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}