I just updated the FAQ entry on online upgrading to be a bit more current, and to include the necessary code from task T151833 since it's no longer a "workaround", it's just a necessary part of the process.
But then I noticed: The instructions are, effectively, to unpack the new version into a separate directory, transfer the locally-modified files over from the old installation to the new one, set the wiki read-only in the old directory, and then "Run the update script or the web updater in the new directory." before swapping the new directory in for the old.
How are you supposed to run the web updater from the new directory, before swapping it in as the live configuration? It's (presumably) not reachable via the webserver, unless the user also modified their server configuration to make it available (something the instructions never even hint at).
Seems to me, running the online update tool necessarily has to wait until after the new directory is made live, which sort of defeats the purpose of performing the update while the wiki remains online.
I get the impression someone shoehorned the web updater into these instructions at some point, because they want to present it as an alternative to using update.php
for maintenance tasks. But this particular procedure really does rely (even hinge) on performing the (live) update via the command-line script, rather than the web updater.