bug#65267: 30.0.50; modifying debug-ignored-errors during startup with --debug-init is broken

[Eli Zaretskii]

> Cc: Stefan Monnier <monnier@iro.umontreal.ca>
> From: Štěpán Němec
>  <stepnem@smrk.net>
> Date: Sun, 13 Aug 2023 09:54:29 +0200
> 
> 
> sh(1) reproduction recipe:
> 
> --8<--
> initdir=$(mktemp -d)
> 
> echo "(add-to-list 'debug-ignored-errors 'my-error)" >"$initdir"/init.el
> emacs --debug-init --init-dir="$initdir" \
>       --eval '(message "%S" debug-ignored-errors)'
> 
> rm -rf "$initdir"
> --8<--
> 
> In the emacs thus started, the value of `debug-ignored-errors' is
> "(my-error startup--witness)" instead of `my-error' added to
> the default ignored error symbol list.

I believe this is a feature: when the user says --debug-init, they
need to be shown all the errors raised during startup; hiding some of
the errors was a misfeature in previous versions of Emacs, now fixed.