GTK4's filters models swallow the reference.
Without this calls crashes like this:
```
#0 g_type_check_instance (type_instance=type_instance@entry=0x555c0f84ce90) at ../../../gobject/gtype.c:4024
#1 0x00007f0837af6e18 in g_signal_handlers_disconnect_matched
(instance=0x555c0f84ce90, mask=mask@entry=(G_SIGNAL_MATCH_FUNC | G_SIGNAL_MATCH_DATA), signal_id=signal_id@entry=0, detail=detail@entry=0, closure=closure@entry=0x0, func=func@entry=0x7f0836f828a0 <gtk_filter_list_model_items_changed_cb>, data=0x555c0f84f1b0) at ../../../gobject/gsignal.c:3007
#2 0x00007f0836f82459 in gtk_filter_list_model_clear_model (self=self@entry=0x555c0f84f1b0 [GtkFilterListModel]) at ../../../gtk/gtkfilterlistmodel.c:497
#3 0x00007f0836f824f4 in gtk_filter_list_model_clear_model (self=0x555c0f84f1b0 [GtkFilterListModel]) at ../../../gtk/gtkfilterlistmodel.c:493
#4 gtk_filter_list_model_dispose (object=0x555c0f84f1b0 [GtkFilterListModel]) at ../../../gtk/gtkfilterlistmodel.c:661
#5 0x00007f0837ae1289 in g_object_unref (_object=0x555c0f84f1b0) at ../../../gobject/gobject.c:4438
#6 0x00007f08379b47f3 in g_hash_table_remove_all_nodes (hash_table=hash_table@entry=0x555c0f84d2c0, notify=notify@entry=1, destruction=destruction@entry=1)
at ../../../glib/ghash.c:656
#7 0x00007f08379b53a3 in g_hash_table_remove_all_nodes (hash_table=0x555c0f84d2c0, notify=1, destruction=1) at ../../../glib/ghash.c:578
#8 g_hash_table_unref (hash_table=0x555c0f84d2c0) at ../../../glib/ghash.c:1438
#9 g_hash_table_unref (hash_table=0x555c0f84d2c0) at ../../../glib/ghash.c:1432
#10 0x0000555bf0b649b2 in calls_manager_finalize (object=0x555c0f84b800 [CallsManager]) at ../src/calls-manager.c:465
#11 0x00007f0837ae14fe in g_object_unref (_object=0x555c0f84b800) at ../../../gobject/gobject.c:4509
#12 0x0000555bf0b5b92d in finalize (object=0x555c0f82fcb0 [CallsApplication]) at ../src/calls-application.c:780
#13 0x00007f0837ae14fe in g_object_unref (_object=0x555c0f82fcb0) at ../../../gobject/gobject.c:4509
#14 0x0000555bf0b58cd4 in main (argc=1, argv=0x7fffc05d57a8) at ../src/main.c:47
```
Steps to reproduce:
- start calls
- open account dialog
- close account dialog
- hit control-c to end calls daemon
- observe above crash
Signed-off-by: Guido Günther <agx@sigxcpu.org>
Part-of: <https://gitlab.gnome.org/GNOME/calls/-/merge_requests/777>
