modify cache directory name to account for / in platform name

.github/workflows/docker-images.yml

@@ -32,13 +32,23 @@ jobs:
         password: ${{ secrets.GHCR_TOKEN }}
         logout: false 
 
+    - name: Create a variable with platform '${{ matrix.platform }}' value
+      run: echo "PLATFORM=${{ matrix.platform }}" >> $GITHUB_ENV
+
+    - name: Swap / for - in '${{ matrix.platform }}' and create local_platform variable
+      id: local_platform
+      run: |
+        LOCAL_PLATFORM="${PLATFORM//\/\-}"
+        echo "LOCAL_PLATFORM=${LOCAL_PLATFORM}" >> $GITHUB_ENV
+        echo "::set-output name=local_platform::${LOCAL_PLATFORM}"
+
     - name: Cache Docker layers
       uses: actions/cache@v3
       with:
         path: /tmp/.buildx-cache
-        key: ${{ runner.os }}-${{ matrix.platform }}-buildx-${{ github.sha }}
+        key: ${{ runner.os }}-${{ steps.local_platform.outputs.local_platform }}-buildx-${{ github.sha }}
         restore-keys: |
-          ${{ runner.os }}-${{ matrix.platform }}-buildx-
+          ${{ runner.os }}-${{ steps.local_platform.outputs.local_platform }}-buildx-
 
     - name: Set up QEMU
       uses: docker/setup-qemu-action@v3