TL 2023 update-tlmgr-latest.sh under Docker fails

[Karl Berry]

    https://github.com/pandoc/dockerfiles/blob/master/common/latex/install-texlive.sh
    Seems pretty vanilla, 

Yep.

    it also has a symlink to that dir called /opt/texlive/texdir/bin/default

I wonder what created that symlink. I don't think it's anything that
install-tl would do. Anyway, I'll change our upgrade script to ignore
such a "bin/default" entry.

Glad Chemnitz worked out. Yay for multiple mirrors! --happy TeXing, karl.