[polari] Update to new accessible API

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

commit fd361e73c2175e89169972eb758298b868704d1f
Author: Florian Müllner <fmuellner gnome org>
Date:   Fri Sep 25 19:59:15 2020 +0200

    Update to new accessible API
    
    Part-of: <https://gitlab.gnome.org/GNOME/polari/-/merge_requests/228>

 src/mainWindow.js | 3 ++-
 src/roomList.js   | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/src/mainWindow.js b/src/mainWindow.js
index 81e6dca0..00cc761c 100644
--- a/src/mainWindow.js
+++ b/src/mainWindow.js
@@ -391,7 +391,8 @@ export default GObject.registerClass({
         let accessibleName = vprintf(ngettext(
             '%d user',
             '%d users', numMembers), numMembers);
-        this._showUserListButton.get_accessible().set_name(accessibleName);
+        this._showUserListButton.update_property(
+            [Gtk.AccessibleProperty.LABEL], [accessibleName]);
         this._showUserListButton.label = `${numMembers}`;
     }
 
diff --git a/src/roomList.js b/src/roomList.js
index 04daed72..f2151ae5 100644
--- a/src/roomList.js
+++ b/src/roomList.js
@@ -415,7 +415,8 @@ const RoomListHeader = GObject.registerClass({
             parent.invalidate_sort();
 
         let accessibleName = vprintf(_('Network %s has an error'), this._account.display_name);
-        this.get_accessible().set_name(accessibleName);
+        this.update_property(
+            [Gtk.AccessibleProperty.LABEL], [accessibleName]);
     }
 
     _getConnectionStatus() {