Update rust/ql/lib/change-notes/2025-09-19-parameter-mad.md

Author: hvitved

rust/ql/lib/change-notes/2025-09-19-parameter-mad.md

@@ -3,5 +3,5 @@ category: feature
 ---
 * The models-as-data format for sources now supports access paths of the form
   `Argument[i].Parameter[j]`. This denotes that the source passes tainted data to
-  the `j`th parameter of it's `i`th argument (which must be a function or a
+  the `j`th parameter of its `i`th argument (which must be a function or a
   closure).