WebEngine fails to load urls from resources

Following the changes to mime-info handling introduced by https://codereview.qt-project.org/c/qt/qtbase/+/328240, I have found that WebEngine can no longer load html urls from internal resources (i.e. using the qrc scheme). I first noticed this when the change was back-ported to 5.15.2 on my archlinux system, but it also affects 6.2.0.

I have attached a test-case that reproduces the problem. To try it, run:

tar -xf testcase.tar.gz
qmake6 testcase.pro && make
./testcase

On my system, the QTextBrowser at the top displays the html, but the QWebEngineView below does not. However, if I run either of these:

./testcase text.html
./testcase qrc:/test.js

the contents are displayed correctly in both widgets. So it seems that only html pages loaded from resources are affected by this issue. When I roll back to a Qt version without the changes introduced by the above mentioned commit, the problem goes away.

I have already reported the problem on the archlinux tracker (https://bugs.archlinux.org/task/72366#comment202803), and it does not appear to be a packaging-related issue.