bug#70039: 30.0.50; list-packages install: Invalid read syntax: "#"

[Stefan Monnier]

> got this new error today when trying to install a package with M-x
> list-packages.
>
> When I revert this commit:
>
>   7e32e8392ab "Fix recent test regressions"
>   (Stefan Monnier <monnier@iro.umontreal.ca> 2024-03-22)
>
> the problem disappears.  This commit causes a destruction of my custom
> file when it gets pp-filled, by adding newlines into #N# syntaxes, like
> #1# => #1\n#.

I pushed a patch to `master` which should fix this problem, but ... this
is nasty.  I was thinking "how quickly one forgets how hard it is to
parse backward" (thinking back to the time where I worked on
`comment-backward`), but while testing I came across a similar problem
that occurs because of the (forward) `scan-sexps` behavior, so it's even
worse than that.


        Stefan