[FIX] tests: move post_install only warning into browser_js

This warning should only appear when Chrome is used.

closes odoo/odoo#48009

X-original-commit: 013b32f000520217af17b6e1ffe1872ec97afdf0
Signed-off-by: Xavier Dollé (xdo) <xdo@odoo.com>
Signed-off-by: Christophe Monniez (moc) <moc@odoo.com>