bug#65700: time when gcs-done is updated needs to be clarified

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Eli Zaretskii <eliz@gnu.org>,  "65700@debbugs.gnu.org"
>  <65700@debbugs.gnu.org>
> Date: Thu, 07 Sep 2023 10:58:46 -0400
> 
> FWIW, I tend to agree that it would be more useful to run `post-gc-hook`
> after those values have been updated.  So that `post-gc-hook` can know
> the exact duration of the GC that we just finished, rather than the one
> before that.
> 
> Any objection to the patch below?

None here, but please call out this incompatible change in NEWS.