ci(cache): whoops, use right version

.github/workflows/pytest.yml

@@ -43,7 +43,7 @@ jobs:
           key: docker-${{ runner.os }}-${{ hashFiles('docker-compose.yaml') }}
 
       - name: Cache Docker layers
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: /tmp/.buildx-cache
           key: ${{ runner.os }}-single-buildx-${{ github.sha }}