There's a merged pull request on the void-packages repository

qutebrowser: update to 3.0.0, use Qt6 by default
https://github.com/void-linux/void-packages/pull/45665

Description:
We can make Qt6 a (default, when possible) build option to allow people to build Qt5 versions if desired, and also force the WebKit backend (which implies Qt5) when WebEngine is unavailable.

#### Testing the changes
- I tested the changes in this PR: **briefly** (I'm using it now)

cc: @daniel-eys