QMimeDatabase: update freedesktop.org.xml to shared-mime-info 2.3

... and update the unittest accordingly.

Compared to the 2.3 release there 2 fixes in freedesktop.org.xml,
due to issues discovered when running tst_qmimedatabase:
* Give higher priority to the more specific image/apng magic
https://gitlab.freedesktop.org/xdg/shared-mime-info/-/merge_requests/262
* Lower priority for text/x-mpsub's magic
https://gitlab.freedesktop.org/xdg/shared-mime-info/-/merge_requests/263

Task-number: QTBUG-118616
Change-Id: I56053b343619a8a711af28e6490c160d13169734
Reviewed-by: Liang Qi <liang.qi@qt.io>
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>