CI: Bump codecov/codecov-action from v3 to v4 (#1491)

See njzjz-bot/njzjz-bot#1.

Co-authored-by: Jinzhe Zeng <jinzhe.zeng@rutgers.edu>

Author: njzjz-bot

.github/workflows/test.yml

@@ -21,7 +21,9 @@ jobs:
       run: pip install -e .[test]
     - name: Test
       run: coverage run --source=./dpgen -m unittest -v && coverage report
-    - uses: codecov/codecov-action@v3
+    - uses: codecov/codecov-action@v4
+      env:
+        CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
   pass:
     needs: [build]
     runs-on: ubuntu-latest