For #6748 Move Add search engine to search engine preference category. (#6749)

app/src/main/res/xml/search_preferences.xml

@@ -12,17 +12,17 @@
         <org.mozilla.fenix.settings.search.RadioSearchEngineListPreference
             android:key="@string/pref_key_search_engine_list"
             android:selectable="false"/>
+        <Preference
+            android:key="@string/pref_key_add_search_engine"
+            android:title="@string/search_engine_add_custom_search_engine_title"
+            android:layout="@layout/preference_search_add_engine"/>
     </PreferenceCategory>
 
     <PreferenceCategory
         android:title="@string/preferences_search_address_bar"
         android:selectable="false"
-        app:iconSpaceReserved="false">
-
-        <Preference
-            android:key="@string/pref_key_add_search_engine"
-            android:title="@string/search_engine_add_custom_search_engine_title"
-            android:layout="@layout/preference_search_add_engine"/>
+        app:iconSpaceReserved="false"
+        app:allowDividerAbove="false">
         <SwitchPreference
             android:defaultValue="true"
             android:key="@string/pref_key_show_search_shortcuts"