ci: downgrade codecov action dependency to v3 (#268)

Author: erisu

.github/workflows/ci.yml

@@ -48,6 +48,6 @@ jobs:
         env:
           CI: true
 
-      - uses: codecov/codecov-action@v4
+      - uses: codecov/codecov-action@v3
         with:
           fail_ci_if_error: true