add PHP 8.1 build step

.github/workflows/php81.yml

@@ -0,0 +1,57 @@
+name: Build 8.1 Image
+on:
+  push:
+    branches: [ 8.1 ]
+  schedule:
+    - cron: '0 10 * * TUE'
+env:
+  PHP_VERSION: 8.1
+  UBUNTU_VERSION: 22.04
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+jobs:
+
+  build:
+    name: Build image
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          ref: ${{ env.PHP_VERSION }}
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v2
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+
+      - name: Log in to the Container registry
+        uses: docker/login-action@v2
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@v4
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v4
+        with:
+          build-args: |
+            php_version=${{ env.PHP_VERSION }}
+            ubuntu_version=${{ env.UBUNTU_VERSION }}
+          context: .
+          labels: ${{ steps.meta.outputs.labels }}
+          platforms: linux/amd64,linux/arm64
+          pull: true
+          push: true
+          tags: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:${{ env.PHP_VERSION }}