main-window.ui: add a proper callback for Close button

The signal click of Close button is connected to "gtk_widget_hide".
As a result the window is hided, but still active and the whole
program renders unresponsive.

The Close button can appear for example if USSD_STATUS_IDLE comes
before a user press Cancel button in dialog window
(could be for example because of carrier timeout).
The "adw_dialog_close" function should be called instead.

Signed-off-by: knoppix <knoppix@4d2.org>
Part-of: <https://gitlab.gnome.org/GNOME/calls/-/merge_requests/776>

src/ui/main-window.ui

@@ -85,7 +85,7 @@
                 <property name="focus-on-click">False</property>
                 <property name="use-underline">True</property>
                 <property name="label" translatable="yes">_Close</property>
-                <signal name="clicked" handler="gtk_widget_hide" object="ussd_dialog" swapped="yes"/>
+                <signal name="clicked" handler="adw_dialog_close" object="ussd_dialog" swapped="yes"/>
               </object>
             </child>
             <child type="end">