Change cache key to use Cargo files

.github/workflows/ci.yml

@@ -52,12 +52,12 @@ jobs:
       - uses: docker/setup-buildx-action@v2
         with:
           driver-opts: network=host
-        # cache slightly improves rebuild time
+        # improve rebuild speeds
       - name: Cache Docker layers
         uses: actions/cache@v3
         with:
           path: /tmp/.buildx-cache
-          key: ${{ runner.os }}-buildx-${{ github.sha }}
+          key: ${{ runner.os }}-buildx-${{ hashFiles('Cargo.toml', 'Cargo.lock') }}
           restore-keys: |
             ${{ runner.os }}-buildx-
       - name: Login to DockerHub