Change cache key for docker action

Signed-off-by: trivernis <trivernis@protonmail.com>

.github/workflows/docker.yml

@@ -25,7 +25,7 @@ jobs:
         uses: actions/cache@v2
         with:
           path: /tmp/.buildx-cache
-          key: ${{ runner.os }}-buildx-${{ github.sha }}
+          key: ${{ runner.os }}-buildx-${{ hashFiles('Cargo.lock') }}
           restore-keys: |
             ${{ runner.os }}-buildx-
       -