Is there a different way to update checkout that everyone else uses?
Not sure who you are referring to in "everyone" -- is it (most) Swift developers or is it (most) Swift toolchain developers? For the latter, most people working on the toolchain work on main, and at the moment, some changes need to be cherry-picked to release/5.5. For the toolchain in Xcode 13 beta, that is based off release/5.5, and the toolchain in Xcode 12.x is based off release/5.4.
If you specifically want the swift-5.4.2 release you need to checkout using --tag instead of --scheme. ./utils/update-checkout --tag swift-5.4.2-RELEASE