build: Update codecov and use token

Update codecov to the latest version and start using the org-wide token for uploads.

See openedx/wg-frontend#179

Author: arbrandes

.github/workflows/ci.yml

@@ -44,7 +44,8 @@ jobs:
 
       - name: Run Coverage
         if: matrix.python-version == '3.8' && matrix.toxenv=='django42-celery53-drflatest'
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
+          token: ${{ secrets.CODECOV_TOKEN }}
           flags: unittests
           fail_ci_if_error: true