[FIX] theme_test_custo: add bigger timeout to the new test

New test was introduced with [1] but it actually sometimes lead to
timeout errors.
That's a common issue since we merged the frontend in the backend and
some tour (like this one) now have to start both the backend and the
frontend (in the iframe).

10 seconds is not enough to load both, it often miss just half a second.

[1]: https://github.com/odoo/design-themes/commit/0e2497b8e84eab8957028f4d63ff0899a9fe6ab3

runbot-4684

closes odoo/design-themes#587

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

theme_test_custo/static/tests/tours/theme_menu_hierarchies.js

@@ -9,6 +9,7 @@ wTourUtils.registerEditionTour('theme_menu_hierarchies', {
     {
         content: 'Check Mega Menu is correctly created',
         trigger: 'iframe #top_menu a.o_mega_menu_toggle',
+        timeout: 20000,
     }, {
         content: 'Check Mega Menu content',
         trigger: 'iframe #top_menu div.o_mega_menu.show .fa-cube',