Qt 6.8 now requires macOS 12.0 as per https://doc.qt.io/qt-6.8/macos.html
for comparison, Qt 6.7 supported 11.0 and newer: https://doc.qt.io/qt-6.7/macos.html
also update the Packages project to refuse to install on anything older
than Monterey (12.0)
Signed-off-by: Jyrki Gadinger <nilsding@nilsding.org>