[gtk/bilelmoussaoui/since-gi] g-i: add missing since annotation

[Bilal Elmoussaoui <bilelmoussaoui src gnome org>]

commit a0d6c6a333a11a71884d847eb25adb57dbd85fb7
Author: Bilal Elmoussaoui <bil elmoussaoui gmail com>
Date:   Thu Dec 9 20:27:06 2021 +0000

    g-i: add missing since annotation

 gtk/gtktextchild.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gtk/gtktextchild.c b/gtk/gtktextchild.c
index 2976550301..5402a0e449 100644
--- a/gtk/gtktextchild.c
+++ b/gtk/gtktextchild.c
@@ -400,6 +400,8 @@ gtk_text_child_anchor_class_init (GtkTextChildAnchorClass *klass)
  * function [method@Gtk.TextBuffer.create_child_anchor].
  * 
  * Returns: a new `GtkTextChildAnchor`
+ *
+ * Since: 4.6
  **/
 GtkTextChildAnchor*
 gtk_text_child_anchor_new (void)