Blacklist flaky QML WebViewFindText::test_findTextManyMatches

Task-number: QTBUG-56373
Change-Id: I599c02a12a0dfb35bb8b3d1d3abbede1c6498f9e
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

tests/auto/quick/qmltests/BLACKLIST

@@ -21,3 +21,6 @@ windows
 
 [WebEngineViewSource::test_viewSourceURL]
 windows
+
+[WebViewFindText::test_findTextManyMatches]
+*