[IMP] bus: prepare bus tests for websocket introduction

The bus tests rely to heavily on the underlying technology (polling).
In order to keep the test intact in the PR introducing the websockets
in Odoo, let's convert the test to be less technical.

task-2053917

closes odoo/odoo#97975

Related: odoo/enterprise#30360
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>