AppVeyor: enable macOS and Windows pipeline #2263
Description
As of 2026-01-08 both the macOS and Windows pipeline have been disabled. It seems AppVeyor is changing/breaking a number of things at the start of the year.
Lately I also ported the the AppImage pipeline because the Linux image we used was dropped without further notice #2249.
The Windows pipeline seems to be broken due to some reconfiguration / Qt6 migration work (see e75e239).
The macOS pipeline is strange. At same point it started working again for a couple of hours. But apart from this the corresponding macos AppVeyor image can not be found. Other image names from the official doc (https://www.appveyor.com/docs/macos-images-software/) do not work either.