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

@@ -37,7 +37,8 @@ jobs:
 
     - name: Run Coverage
       if: matrix.python-version == '3.8' && matrix.toxenv=='django42'
-      uses: codecov/codecov-action@v3
+      uses: codecov/codecov-action@v4
       with:
+        token: ${{ secrets.CODECOV_TOKEN }}
         flags: unittests
         fail_ci_if_error: true