Reword changelog

CHANGELOG.rst

@@ -26,7 +26,7 @@ Fixed
 * Optimize exam model and add reference to exams at extra lessons.
 * Lessons weren't shown as cancelled on teacher or room timetables
   if events had replaced them.
-* The teacher dropdown field in the substitution edit form did not work.
+* The teacher dropdown in the substitution edit form did not contain suggestions.
 
 `2.3`_ - 2022-03-21
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