[gtksourceview] testwidget: add map class to overview map

[Christian Hergert <chergert src gnome org>]

commit 24308e18b6504899311825278c74d66f12d28918
Author: Christian Hergert <chergert redhat com>
Date:   Thu Oct 14 15:38:17 2021 -0700

    testwidget: add map class to overview map
    
    This just allows playing with CSS styling from the preview.

 tests/test-widget.ui | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/tests/test-widget.ui b/tests/test-widget.ui
index d6c28888..4843e036 100644
--- a/tests/test-widget.ui
+++ b/tests/test-widget.ui
@@ -472,6 +472,9 @@
             <property name="visible">True</property>
             <property name="can_focus">False</property>
             <property name="view">view</property>
+            <style>
+              <class name="map"/>
+            </style>
             <layout>
               <property name="column">2</property>
               <property name="row">0</property>