macOS: Monterey now required

Apr 23, 2024

Previously, we supported Movave (macOS 10.14).

We skipped over Catalina (10.15) and Big Sur (11).

Now, we require Moterey (macOS 12).

Sorry for any inconvenience. The build system has to stay on macOS versions that are supported by Apple an Homebrew; we can sit out updates while there are no changes to requirements and have done so ever since the builds started rolling again, but now an update to the notarization procedure (announced well in advance, no blame on Apple there) broke the old Mojave system. Just for the notarization, an upgrade to Catalina would have been enough, but then there was no way to get working Homebrew builds of the sdl2 libraries we need for that old system, so further upgrades were required.  The current release is still unaffected by this change, a future release will be affected.