tdf#91063 Move border to Gtkbox similar to other panels

Change-Id: I8f385b2997585b3245ad862da60f0b394689b03b
Reviewed-on: https://gerrit.libreoffice.org/19463Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

chart2/uiconfig/ui/sidebarelements.ui

@@ -5,13 +5,13 @@
   <object class="GtkGrid" id="ChartElementsPanel">
     <property name="visible">True</property>
     <property name="can_focus">False</property>
-    <property name="border_width">6</property>
     <child>
       <object class="GtkBox" id="container">
         <property name="visible">True</property>
         <property name="can_focus">False</property>
         <property name="orientation">vertical</property>
         <property name="spacing">6</property>
+        <property name="border_width">6</property>
         <child>
           <object class="GtkFrame" id="frame1">
             <property name="visible">True</property>