[tlu] TeX Live Utility (MacTeX) critical update failure

[Karl Berry]

    ./runme.sh: no xz.[universal-darwin][.exe] binary for 
    /usr/local/texlive/2023/bin/universal-darwin in 
    /var/folders/c9/mqg453cx4bg50wwbqxsr4x0w0000gn/T/selfgz3210124610/installer/xz.

1) Technically tlu at tug.org is a better place to report TLU errors,
although I see Adam is on this list (tex-live). Cc-ing for the heck of it.

2) It's unclear to me why the xz executable is not there for TLU, since
it is there in the repo's .../installer/xz directory:
$ ls -l tlpkg/installer/xz/xz.universal-darwin
-rwxrwxr-x. 1 karl root 451744 Mar  2  2022 tlpkg/installer/xz/xz.universal-darwin*

Also, the self-update worked on (all?) other platforms.

Adam? --thanks, karl.