[polari] roomList: Use .menu style for header popover

[Marge Bot <marge-bot src gnome org>]

commit b5a4ebea99e5fd087d75c07936e5747a784f68c0
Author: Florian Müllner <fmuellner gnome org>
Date:   Thu Mar 17 19:43:48 2022 +0100

    roomList: Use .menu style for header popover
    
    The difference between menu- and custom popovers doesn't matter
    in the default GTK4 style, but it does for the new Adwaita theme.
    
    Part-of: <https://gitlab.gnome.org/GNOME/polari/-/merge_requests/250>

 data/resources/room-list-header.ui | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/data/resources/room-list-header.ui b/data/resources/room-list-header.ui
index 60c65d87..b2f15487 100644
--- a/data/resources/room-list-header.ui
+++ b/data/resources/room-list-header.ui
@@ -92,6 +92,9 @@
     </child>
   </template>
   <object class="GtkPopover" id="connectionPopover">
+    <style>
+      <class name="menu"/>
+    </style>
     <property name="child">
       <object class="GtkBox">
         <property name="orientation">vertical</property>