[FIX]IM Chat:bug with kanban view

Visiblity Bug in Kanban View: The Add button and Dropdown toggle button of Kanban view is visible even if the IM is open above the Kanban View

More Details
Task: https://www.odoo.com/web#id=8701&view_type=form&model=project.task&menu_id=3942&action=327

Pad: https://pad.odoo.com/p/r.p5OMegki6Y3ySALZ