Enhancement (ci): Use separate workflow for PR docker builds

This is so the `docker` workflow status is not polluted with PR builds.

.github/workflows/docker-pr.yml

@@ -0,0 +1,93 @@
+name: docker-pr
+
+on:
+  pull_request:
+    branches:
+    - master
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v3
+
+    # This step generates the docker tags
+    - name: Docker meta
+      id: meta
+      uses: docker/metadata-action@v4
+      env:
+        # This env var ensures {{sha}} is a real commit SHA for type=ref,event=pr
+        DOCKER_METADATA_PR_HEAD_SHA: 'true'
+      with:
+        images: |
+          djmaze/snappymail
+          ghcr.io/${{ github.repository }}
+        # type=ref,event=pr generates tag(s) on PRs only. E.g. 'pr-123', 'pr-123-abc0123'
+        tags: |
+          type=ref,event=pr
+          type=ref,suffix=-{{sha}},event=pr
+        # The rest of the org.opencontainers.image.xxx labels are dynamically generated
+        labels: |
+          org.opencontainers.image.description=SnappyMail
+          org.opencontainers.image.licenses=AGPLv3
+
+    # See: https://github.com/docker/build-push-action/blob/v2.6.1/docs/advanced/cache.md#github-cache
+    - name: Set up QEMU
+      uses: docker/setup-qemu-action@v2
+
+    - name: Set up Docker Buildx
+      id: buildx
+      uses: docker/setup-buildx-action@v2
+
+    - name: Cache Docker layers
+      uses: actions/cache@v3
+      with:
+        path: /tmp/.buildx-cache
+        key: ${{ runner.os }}-buildx-${{ github.sha }}
+        restore-keys: |
+          ${{ runner.os }}-buildx-
+
+    # See: https://github.com/docker/buildx/issues/59
+    - name: Build
+      id: build
+      uses: docker/build-push-action@v3
+      with:
+        context: '.'
+        file: ./.docker/release/Dockerfile
+        platforms: linux/amd64
+        push: false
+        load: true
+        tags: ${{ steps.meta.outputs.tags }}
+        labels: ${{ steps.meta.outputs.labels }}
+        cache-from: type=local,src=/tmp/.buildx-cache
+        cache-to: type=local,dest=/tmp/.buildx-cache-new,mode=max
+
+    - name: Docker images
+      run: |
+        docker images
+
+    - name: Test
+      run: |
+        TAG=$( echo "${{ steps.meta.outputs.tags }}" | head -n1 )
+        .docker/release/test/test.sh "$TAG"
+
+    - name: Build all archs
+      uses: docker/build-push-action@v3
+      with:
+        context: '.'
+        file: ./.docker/release/Dockerfile
+        platforms: linux/386,linux/amd64,linux/arm64
+        push: false
+        tags: ${{ steps.meta.outputs.tags }}
+        labels: ${{ steps.meta.outputs.labels }}
+        cache-from: type=local,src=/tmp/.buildx-cache
+        cache-to: type=local,dest=/tmp/.buildx-cache-new,mode=max
+
+    # Temp fix
+    # https://github.com/docker/build-push-action/issues/252
+    # https://github.com/moby/buildkit/issues/1896
+    - name: Move cache
+      run: |
+        rm -rf /tmp/.buildx-cache
+        mv /tmp/.buildx-cache-new /tmp/.buildx-cache

.github/workflows/docker.yml

@@ -3,10 +3,7 @@ name: docker
 on:
   push:
     tags:
-    - '**'
-  pull_request:
-    branches:
-    - master
+    - 'v2.*'
 
 # This is needed to push to GitHub Container Registry. See https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-container-registry
 permissions:
@@ -31,12 +28,9 @@ jobs:
         images: |
           djmaze/snappymail
           ghcr.io/${{ github.repository }}
-        # type=ref,event=pr generates tag(s) on PRs only. E.g. 'pr-123', 'pr-123-abc0123'
         # type=ref,event=branch generates tag(s) on branch only. E.g. 'master', 'master-abc0123'
         # type=ref,event=tag generates tag(s) on tags only. E.g. 'v0.0.0', 'v0.0.0-abc0123', and 'latest'
         tags: |
-          type=ref,event=pr
-          type=ref,suffix=-{{sha}},event=pr
           type=ref,event=branch
           type=ref,event=tag
         # The rest of the org.opencontainers.image.xxx labels are dynamically generated

README.md

@@ -6,7 +6,7 @@
   <h1>SnappyMail</h1>
   <br>
 
-[![github-actions](https://github.com/the-djmaze/snappymail/workflows/docker/badge.svg)](https://github.com/the-djmaze/snappymail/actions/workflows/docker.yml)
+[![github-actions](https://github.com/the-djmaze/snappymail/actions/workflows/docker.yml/badge.svg)](https://github.com/the-djmaze/snappymail/actions/workflows/docker.yml)
 [![docker-image-size](https://img.shields.io/docker/image-size/djmaze/snappymail/latest)](https://hub.docker.com/r/djmaze/snappymail/tags)
 
   <p>