However, we are missing an entry for Swift 5.4.2 in
Point releases are made from the same branch. For example, the latest commit on the 5.4 branch was to bump the version to 5.4.2. bump version to 5.4.2 by shahmishal · Pull Request #38027 · apple/swift · GitHub
There is a scheme for
release/5.4, so you can use that.
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.