[fix] categories can't be removed from UI (categories_as_tabs)

When using ``use_default_settings: true``, removing default categories from
settings.yml will not remove them from the UI.

The value ``categories_as_tabs`` is a dictionary type (a4c2cfb) and dictionary
types are merged additive by ``settings_loader.update_settings()``.

This patch replaces the default ``categories_as_tabs`` by the one from the
``user_settings``.

Related: https://github.com/searxng/searxng/issues/1019#issuecomment-1193145654
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/settings_loader.py

@@ -74,6 +74,10 @@ def update_settings(default_settings, user_settings):
             else:
                 default_settings[k] = v
 
+    categories_as_tabs = user_settings.get('categories_as_tabs')
+    if categories_as_tabs:
+        default_settings['categories_as_tabs'] = categories_as_tabs
+
     # parse the engines
     remove_engines = None
     keep_only_engines = None