[FIX] web: nightly clickall timeouts

The nightly clickall runbot fail due to a crash of the underlying chrome
browser used to run the test suite. The problem is related to the
resources the browser is using. We leverage the problem by starting one
dedicated browser per app.

closes odoo/odoo#39135

Signed-off-by: Xavier Dollé (xdo) <xdo@odoo.com>