In PR #3292 we move from macos-11 to macos-12 because of the deprecation of macos-11 by Github.

In macos-12, the earliest versions of xcode available are 13.x.x. These versions fail by default if the project uses the "legacy build system".

PR #3292 includes a configuration setting to suppress the failure and deprecation warning, so that the build succeeds.

The "legacy build system" is completely removed in xcode 14, and so we need to update the iOS build to use the newer xcode "modern build system".