devel/kf5-kio: backport regression-fixes from upstream

Upstream reports that the following three commits should be
backported for improved performance and accuracy for
mimetype detection in KIO-using applications:

(In https://invent.kde.org/frameworks/kio/commit/)
c748d6987252fafc296cde9351b289ef734cf861
e79da836c34fce66231e396c7215314d0eba51b4
c19876052ecec18a87a82f5950e8909e22e895ba