chore(ci): cache flutter by commit hash [skip ci]

.github/workflows/clear_flutter_cache.yml

@@ -8,15 +8,12 @@ jobs:
     name: Clear Cache
     runs-on: ubuntu-latest
     steps:
-      - name: generate Unique Key
-        run: echo CACHE_KEY=key-$(date +%s) >> $GITHUB_ENV
-
       - name: Install Flutter
         uses: subosito/flutter-action@v2
         with:
           channel: beta
           cache: true
-          cache-key: ${{ env.CACHE_KEY }}
+          cache-key: ${{ github.sha }}
 
       - name: Flutter Doctor
         working-directory: ${{ github.workspace }}