Update codecov/codecov-action action to v4

Author: renovate[bot]

.github/workflows/ci.yml

@@ -63,7 +63,7 @@ jobs:
         run: composer stan:ci
 
       - name: 📤 Upload coverage report to Codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
           files: ./coverage.xml