[IMP] theme_*: adapt themes tests for the new snippet category

*: artists, avantgarde, aviato, buzzy, orchid, paptic, real_estate,
treehouse, zap

This commit aims to adapt tests within each themes that uses the
`s_three_columns` snippet.

As we introduce the `Columns` category within the snippet modal, we are
moving the `s_three_columns` from the `Content` category to the `Columns`
one. This implies an adaptation of the tests where the `s_three_columns`
was defined as part of the `Content` category.

task-4119460
follow-up of task-3919405

closes odoo/design-themes#872

Related: odoo/odoo#176889
Signed-off-by: Robin Lejeune (role) <role@odoo.com>

theme_treehouse/static/src/js/tour.js

@@ -21,7 +21,7 @@ const snippets = [
     {
         id: 's_three_columns',
         name: 'Columns',
-        groupName: "Content",
+        groupName: "Columns",
     },
     {
         id: 's_call_to_action',