 style_callback param for add_geojson() not working?

### Environment Information

-   geemap version: 0.9.2
-   Python version: 3.9
-   Operating System: Linux/macOS

### Description

Essentially the same as https://github.com/giswqs/leafmap/issues/119.

<img width="757" alt="Screen Shot 2021-10-03 at 23 28 34" src="https://user-images.githubusercontent.com/1001778/135772216-93a49766-5bb9-49ad-af07-6067610d2abf.png">

