[gtk] testsuite/gtk/flattenlistmodel.c: fix build

[Marc-Antoine Perennou <marcop src gnome org>]

commit eb8e0910c321ffdd3104a3ea3e5c034782bb9d46
Author: Marc-Antoine Perennou <Marc-Antoine Perennou com>
Date:   Sun Mar 22 10:53:59 2020 +0100

    testsuite/gtk/flattenlistmodel.c: fix build
    
    Signed-off-by: Marc-Antoine Perennou <Marc-Antoine Perennou com>

 testsuite/gtk/flattenlistmodel.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/testsuite/gtk/flattenlistmodel.c b/testsuite/gtk/flattenlistmodel.c
index 8851097dc5..dd56e37464 100644
--- a/testsuite/gtk/flattenlistmodel.c
+++ b/testsuite/gtk/flattenlistmodel.c
@@ -307,7 +307,7 @@ static void
 test_submodel_add2 (void)
 {
   GtkFlattenListModel *flat;
-  GListStore *model, *store[2];
+  GListStore *model, *store[3];
 
   model = g_list_store_new (G_TYPE_LIST_MODEL);
   flat = new_model (model);