Update CHANGELOG.md

Added PR python-qt-tools#50 description

Author: Djedouas

CHANGELOG.md

@@ -9,6 +9,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Added
 
 ### Changed
+* [#50](https://github.com/stlehmann/PyQt5-stubs/pull/50) fixes QTest QAbstractItemModelTester.FailureReportingMode attributes
 * [#46](https://github.com/stlehmann/PyQt5-stubs/pull/46) fixes QCoreApplication and QObject signals
 * [#48](https://github.com/stlehmann/PyQt5-stubs/pull/48) fixes some signals for QClipBoard, QWindows, QQuickView and QQml{Application,}Engine
 * [#49](https://github.com/stlehmann/PyQt5-stubs/pull/49) fixes QAbstractItemView.setModel to accept None