Enabling docker build (no push) on PR

.github/workflows/docker.yml

@@ -4,6 +4,9 @@ on:
   push:
     branches:
       - 'master'
+  pull_request:
+    branches:
+      - '**'
 
 jobs:
   docker_deps:
@@ -15,7 +18,8 @@ jobs:
     #    $ sudo apt-get upgrade qemu-user-static
     #    $ docker run --rm --privileged multiarch/qemu-user-static --reset -p yes -c yes
     # More info: https://github.com/introlab/rtabmap/issues/1454
-    # if: false
+    # Skipped on pull requests; built and pushed only on push to master.
+    if: github.event_name != 'pull_request'
 
     runs-on: ubuntu-latest
     
@@ -85,6 +89,8 @@ jobs:
   
   docker:
     needs: docker_deps
+    # Run even when docker_deps is skipped (it is, on pull requests).
+    if: ${{ !cancelled() && !failure() }}
     runs-on: ubuntu-latest
     
     strategy:
@@ -190,6 +196,9 @@ jobs:
         uses: docker/setup-buildx-action@v3
       -
         name: Login to DockerHub
+        # Only needed when pushing; skipped on pull requests (secrets are
+        # unavailable for fork PRs and we don't push there anyway).
+        if: github.event_name != 'pull_request'
         uses: docker/login-action@v3
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
@@ -199,8 +208,8 @@ jobs:
         uses: docker/build-push-action@v6
         with:
           context: .
-          push: true
-          platforms: ${{ matrix.docker_platforms }}
+          push: ${{ github.event_name != 'pull_request' }}
+          platforms: ${{ github.event_name == 'pull_request' && 'linux/amd64' || matrix.docker_platforms }}
           file: ./docker/${{ matrix.docker_path }}/Dockerfile
           build-args: |
             ${{ matrix.docker_args }}