--preset="buildbot_osx_package"だからアサーションついてるぽい。 https://ci.swift.org/view/Swift%205.3/job/oss-swift-5.3-package-osx/
[preset: buildbot_osx_package] mixin-preset= mixin_osx_package_base mixin_osx_package_test mixin_lightweight_assertions,no-stdlib-asserts … # A mixin that enables 'lightweight' assertions that don't slow down the # compiler significantly. [preset: mixin_lightweight_assertions] assertions
https://github.com/apple/swift/blob/main/utils/build-presets.ini#L1306-L1310