Added CHANGELOG.md entry

Author: TilmanK

CHANGELOG.md

@@ -23,6 +23,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 * [#184](https://github.com/python-qt-tools/PyQt5-stubs/pull/184) Fix missing module variable
    detected by latest mypy 0.930
 * [#183](https://github.com/python-qt-tools/PyQt5-stubs/pull/183) Add missing operations on QSize
+* [#189](https://github.com/python-qt-tools/PyQt5-stubs/pull/189) Fix QListWidget, QTreeWidget and QTableWidget so that their respective items are now optional in many places when used as argument or return value
 ## 5.15.2.0
 
 ### Added