ci: revert to codecov-action v3

Author: danielroe

.github/workflows/test.yml

@@ -151,7 +151,7 @@ jobs:
         run: yarn test:unit --coverage
 
       - name: codecov
-        uses: codecov/codecov-action@v4
+        uses: codecov/codecov-action@v3
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
           flags: unittests