[gtk/wip/exalm/nullable] widget: Add missing (nullable) on binding functions

[Alexander Mikhaylenko <alexm src gnome org>]

commit 31a072497d2a7d16cc25805a26d7b4d9a1a7c43a
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Tue Oct 20 16:26:17 2020 +0500

    widget: Add missing (nullable) on binding functions
    
    Even though they are marked as (skip), they are used in Vala and have wrong
    types there atm.

 gtk/gtkwidget.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index 29f595c55a..7a1a0eed71 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -4073,7 +4073,7 @@ gtk_widget_real_size_allocate (GtkWidget *widget,
  * @keyval: key value of binding to install
  * @mods: key modifier of binding to install
  * @callback: the callback to call upon activation
- * @format_string: GVariant format string for arguments or %NULL for
+ * @format_string: (nullable): GVariant format string for arguments or %NULL for
  *     no arguments
  * @...: arguments, as given by format string.
  *
@@ -4122,7 +4122,7 @@ gtk_widget_class_add_binding (GtkWidgetClass  *widget_class,
  * @keyval: key value of binding to install
  * @mods: key modifier of binding to install
  * @signal: the signal to execute
- * @format_string: GVariant format string for arguments or %NULL for
+ * @format_string: (nullable): GVariant format string for arguments or %NULL for
  *     no arguments
  * @...: arguments, as given by format string.
  *
@@ -4171,7 +4171,7 @@ gtk_widget_class_add_binding_signal (GtkWidgetClass  *widget_class,
  * @keyval: key value of binding to install
  * @mods: key modifier of binding to install
  * @action_name: the action to activate
- * @format_string: GVariant format string for arguments or %NULL for
+ * @format_string: (nullable): GVariant format string for arguments or %NULL for
  *     no arguments
  * @...: arguments, as given by format string.
  *