luametatex needs an update

[Karl Berry]

    Related to what Max said in the later email: I don't see any
    particular reason why we couldn't upgrade one broken binary.

For the particular situation of luametatex, I agree.

    (I can volunteer to take care of it 

Thanks. Gratefully accepted.

    if I get a thumbs-up from Karl.)

+1 from me.

     when is the moment to [commit]

Any time. As long as we're not adding or removing files, the
infrastructure will just notice the new revision number from the commit
and make new platform-specific packages with the new binaries.
E.g., they don't all have to be committed at the same time.

    - Asking other builders for a new binary for macOS, Cygwin, NetBSD

Yep. When it's time, please write tlbuild with a pointer to the source
that they're supposed to compile. --thanks for all, karl.