Use a ghaction matrix in docker build

to build each architecture individually

.github/workflows/build.yml

@@ -1,8 +1,5 @@
 name: Docker builds
 
-env:
-  TARGET_PLATFORMS: linux/amd64,linux/arm/v6,linux/arm/v7,linux/arm64
-
 on:
   schedule:
     - cron: "0 10 * * *" # everyday at 10am
@@ -17,6 +14,15 @@ jobs:
   build:
     name: Build and deploy docker images
     runs-on: ubuntu-20.04
+    
+    strategy:
+      matrix:
+        target_platform:
+          - "linux/amd64"
+          - "linux/arm/v6"
+          - "linux/arm/v7"
+          - "linux/arm64"
+    
     steps:
       - name: Checkout
         uses: actions/checkout@v2
@@ -26,14 +32,14 @@ jobs:
         id: cache
         with:
           path: /tmp/.buildx-cache
-          key: ${{ runner.os }}-buildx-${{ secrets.CACHE_KEY }}-${{ github.sha }}
+          key: ${{ runner.os }}-buildx-${{ secrets.CACHE_KEY }}-${{ matrix.target_platform }}-${{ github.sha }}
           restore-keys: |
-            ${{ runner.os }}-buildx-${{ secrets.CACHE_KEY }}-
+            ${{ runner.os }}-buildx-${{ secrets.CACHE_KEY }}-${{ matrix.target_platform }}-
 
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v1
         with:
-          platforms: ${{ env.TARGET_PLATFORMS }}
+          platforms: ${{ matrix.target_platform }}
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v1
@@ -43,7 +49,7 @@ jobs:
         run: |
           DOCKER_USERNAME=viktorstrate
           DOCKER_IMAGE=viktorstrate/photoview
-          DOCKER_PLATFORMS=${TARGET_PLATFORMS}
+          DOCKER_PLATFORMS=${{ matrix.target_platform }}
           VERSION=edge
 
           if [[ $GITHUB_REF == refs/tags/* ]]; then