[mutter] clutter/content: Mark optional parameters as such in annotation

[Marge Bot <marge-bot src gnome org>]

commit e25df6675a352e4e37b7f46f015a4928e2ad1054
Author: Sebastian Keller <skeller gnome org>
Date:   Mon Nov 8 04:50:14 2021 +0100

    clutter/content: Mark optional parameters as such in annotation
    
    The width and height parameters of clutter_content_get_preferred_size()
    are optional, but were not marked as such. With a current gjs this will
    result in a warning if a caller does not use them.
    
    Found by Evan Welsh
    
    Fixes: https://gitlab.gnome.org/GNOME/mutter/-/issues/1945
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2079>

 clutter/clutter/clutter-content.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/clutter/clutter/clutter-content.c b/clutter/clutter/clutter-content.c
index 31abd1135c..92f485d74c 100644
--- a/clutter/clutter/clutter-content.c
+++ b/clutter/clutter/clutter-content.c
@@ -322,8 +322,8 @@ _clutter_content_paint_content (ClutterContent      *content,
 /**
  * clutter_content_get_preferred_size:
  * @content: a #ClutterContent
- * @width: (out): return location for the natural width of the content
- * @height: (out): return location for the natural height of the content
+ * @width: (out) (optional): return location for the natural width of the content
+ * @height: (out) (optional): return location for the natural height of the content
  *
  * Retrieves the natural size of the @content, if any.
  *