[glib: 1/2] docs: Fix annotations for optional arguments

[Philip Withnall <pwithnall src gnome org>]

commit 708100c0a22c78340129018088471b57f697afdc
Author: Evangelos Ribeiro Tzaras <devrtz fortysixandtwo eu>
Date:   Fri Jun 11 15:19:17 2021 +0200

    docs: Fix annotations for optional arguments
    
    The length parameter in g_hash_table_get_keys_as_arrays() is optional and
    this should be reflected in the gtk-doc annotations.

 glib/ghash.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/glib/ghash.c b/glib/ghash.c
index cc2d00087..48a7db0e2 100644
--- a/glib/ghash.c
+++ b/glib/ghash.c
@@ -2191,7 +2191,7 @@ g_hash_table_get_keys (GHashTable *hash_table)
 /**
  * g_hash_table_get_keys_as_array:
  * @hash_table: a #GHashTable
- * @length: (out): the length of the returned array
+ * @length: (out) (optional): the length of the returned array
  *
  * Retrieves every key inside @hash_table, as an array.
  *