[gtksourceview/gtksourceview-4-6] styleschememanager: fix annotation

[Christian Hergert <chergert src gnome org>]

commit cd980a84c4d42c1903c283b232e3dd3d670691a0
Author: Christian Hergert <chergert redhat com>
Date:   Wed May 13 18:59:33 2020 -0700

    styleschememanager: fix annotation
    
    Fixes #133

 gtksourceview/gtksourcestyleschememanager.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/gtksourceview/gtksourcestyleschememanager.c b/gtksourceview/gtksourcestyleschememanager.c
index c56d09bc..bea622f1 100644
--- a/gtksourceview/gtksourcestyleschememanager.c
+++ b/gtksourceview/gtksourcestyleschememanager.c
@@ -572,8 +572,8 @@ gtk_source_style_scheme_manager_get_scheme_ids (GtkSourceStyleSchemeManager *man
  *
  * Looks up style scheme by id.
  *
- * Returns: (transfer none): a #GtkSourceStyleScheme object. Returned value is owned by
- * @manager and must not be unref'ed.
+ * Returns: (transfer none) (nullable): a #GtkSourceStyleScheme object.
+ *   The returned value is owned by @manager and must not be unref'ed.
  */
 GtkSourceStyleScheme *
 gtk_source_style_scheme_manager_get_scheme (GtkSourceStyleSchemeManager *manager,