update to v4 and add token (#360)

v4 requires tokens now

Author: tasansal

.github/workflows/tests.yml

@@ -152,4 +152,6 @@ jobs:
           nox --session=coverage -- xml
 
       - name: Upload coverage report
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}