[FIX] mail: do not refocus search bar on click category bar

Before this commit, when clicking on category in category bar,
the search bar was (re-)focused.

It was flickering, especially when device prompt a soft keyboard,
such as on mobile.

This commit fixes the issue by not (re-)focusing the search bar
when clicking on a category from the category bar.

Task-3013819

closes odoo/odoo#102962

Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>