[polari] mainWindow: Add empty title label to sidebar header

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

commit c2c02cad74ff22f3134cae462de659a5533d8b1d
Author: Florian Müllner <fmuellner gnome org>
Date:   Sun Sep 27 03:52:50 2020 +0200

    mainWindow: Add empty title label to sidebar header
    
    In GTK4, headerbars automatically include the window title (or
    an appropriate fallback). We don't want the title to show in
    both headerbars, so disable the behavior by adding an empty
    label as custom title widget to the left one.
    
    Part-of: <https://gitlab.gnome.org/GNOME/polari/-/merge_requests/225>

 data/resources/main-window.ui | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/data/resources/main-window.ui b/data/resources/main-window.ui
index 604633da..f00e0ae9 100644
--- a/data/resources/main-window.ui
+++ b/data/resources/main-window.ui
@@ -45,6 +45,9 @@
             <property name="visible">True</property>
             <property name="hexpand">False</property>
             <property name="show-close-button">True</property>
+            <child type="title">
+              <object class="GtkLabel"/>
+            </child>
             <child>
               <object class="GtkButton" id="joinButton">
                 <property name="visible">True</property>