Update `trigger_json_event` for Bokeh 3

[Simon Høxbro Hansen]

trigger_json_event no longer exists in Bokeh 3.1.

jupyter_bokeh/jupyter_bokeh/widgets.py

Line 136 in f343b90

 self._document.callbacks.trigger_json_event(content["msg_data"]) 

[Mateusz Paprocki]

I fixed this in PR #178, among other issues related to bokeh 3.