[FIX] website: fix call to action button in off-canvas menu

When the navbar hamburger type option is set to 'off-canvas', the 'call
to action' button of the 'boxed' header is located "next to" the navbar
instead of "in" the navbar as it should be.

This commit puts the 'call to action' button in the navbar when the
'off-canvas' menu is opened.

task-3063878

closes odoo/odoo#105768

Signed-off-by: Bojabza Soukéina (sobo) <sobo@odoo.com>