bug#63891: 29.0.91; customize-save-variable should not save all variables if a custom file exists

[Eli Zaretskii]

> From: Michael Albinus <michael.albinus@gmx.de>
> Cc: Jimmy Wong <wyuenho@gmail.com>,  63891@debbugs.gnu.org
> Date: Tue, 06 Jun 2023 14:01:22 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> Hi Eli,
> 
> >> No it does not saves only one variable to file, it only saves one variable 
> >> to file if you have only modified
> >> one variable.
> >
> > That's not what I see.  I've modified several options using the
> > menu-bar's Options menu, then typed
> >
> >   M-x customize-save-variable RET truncate-lines RET y
> >
> > and saw that only truncate-lines was written to the custom file.
> >
> > If you see something else, please show a complete recipe that
> > reproduces the behavior you see.
> 
> custom-set-variables

That's a different function.  I was talking about
customize-save-variable.