Fix add key to cache step

Author: gilzoide

.github/workflows/build.yml

@@ -25,10 +25,11 @@ jobs:
             target: docker-all-webgl
     steps:
       - uses: actions/checkout@v3
-      - name: Cache SCons files
+      - name: Cache Docker files
         uses: actions/cache@v4
         with:
           path: $DOCKER_CACHE
+          key: ${{ matrix.platform }}
       - name: Build
         run: make -C Plugins ${{ matrix.target }} DOCKER_BUILD_ARGS="--cache-to type=local,dest=$DOCKER_CACHE --cache-from type=local,src=$DOCKER_CACHE"
       - name: Upload artifact