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

[Shynur Xie]

> shynur:
> My Emacs displays its runtime information like this:
>   <github.com/shynur/.emacs.d/issues/1#issuecomment-1671815270>
> Since it's mainly related to GC, I have it updated after each GC.

> Eli:
> That's just causes off-by-one count of GC cycles, no?  Easy enough
> to fix.

> Stefan:
> the only difference is that `gcs-done` will be always smaller by 1

We forgot the `gc-elapsed'.  It's a little hard to fix (dirty work is
needed).