Fix propagation of unhandled key press events

Unhandled key presses for printable keys were not received by the parent
widget anymore. This was a regression from 5.8.0.

The propagation is suppressed if NativeWebKeyboardEvent::skip_in_browser
is true.

Commit 4501b9d8

 accidentally removed the wrong skip_in_browser
assignment.

Task-number: QTBUG-61621
Change-Id: I7eafa1fac5fb9a7edc4af2bc1aac21c106264713
Reviewed-by: Peter Varga <pvarga@inf.u-szeged.hu>