842777ea4a
The macos-14 runner image no longer ships Xcode 16.0; the default is now Xcode 16.4. Pin the runner to that version explicitly so `xcode-select -s /Applications/Xcode_16.4.app` succeeds. Also drops the build matrix `xcode` field, since the runner only has one Xcode available and we do not test across multiple Xcode versions on the audit/appstore-prep branch. Refs: AUDIT_APPSTORE.md P0-1