bug#65797: 29.0.92; func-arity should not return (0 . many) with apply-partially

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Joseph Turner <joseph@breatheoutbreathe.in>,  65797@debbugs.gnu.org
> Date: Fri, 08 Sep 2023 11:52:25 -0400
> 
> >> This isn't backwards compatible, is it?
> > Neither is what you propose, AFAIU.  We are in effect changing a
> > public API in incompatible ways.
> 
> Yup, AFAICT there's no way to implement the Texinfo-documented
> behavior reliably.
> 
> So some backward-incompatibility is inevitable, unless we decide to
> stick to the current code to be "bug compatible" :-(

I think one of the alternatives you proposed was backward-compatible
(albeit not very elegant).  So my vote is for that alternative.