[Qt Virtual Keyboard] Built-in style uses font family that doesn't exist on all platforms

Steps to reproduce
Jun run any project that uses the Qt Virtual Keyboard on macOS using the environment variable, QT_LOGGING_RULES="qt.qpa.fonts=true;"

Outcomes
We see the following debug output:

qt.qpa.fonts: Populating font family aliases took 159 ms. Replace uses of missing font family "Sans" with one that exists to avoid this cost.

Culprit
"Sans" is hard-coded in the default style: https://github.com/qt/qtvirtualkeyboard/blob/v6.7.0-rc1/src/styles/builtin/default/style.qml#L12