[articleviewerwebengine] Reinstate crash "workaround" for Qt 5.13

It seems that this code is still needed, without it Akregator crashes
again here when opening/closing tabs.

Uses SetUrlRequestInterceptor() on 5.13+ instead, as
SetRequestInterceptor() is deprecated.

BUG: 371511

FIXED-IN: 5.11.3
Differential Revision: https://phabricator.kde.org/D22228