bug#63201: `scroll-margin' sometimes doesn't work

[Eli Zaretskii]

> From: Shynur Xie <one.last.kiss@outlook.com>
> Date: Mon, 1 May 2023 10:45:11 +0000
> msip_labels: 
> 
> `scroll-margin' sometimes doesn't work
> 
> 1. emacs -Q
> 2. In buffer *scratch*, C-x C-e:
>     (progn
>       (custom-set-variables
>        '(custom-enabled-themes '(modus-vivendi))
>        '(global-tab-line-mode t)
>        '(scroll-margin 1)
>        '(scroll-conservatively 101))
>       (info-emacs-manual)
>       (end-of-buffer)
>       (goto-line 500))
> 3. With the cursor now at the 2nd line from the top of the window,
>    press <up>-arrow-key several times and pay attention to resulting
>    cursor position -- `scroll-margin' is 1 but Emacs still sometimes
>    allows the cursor to stay at the 1st line of the window.

Thanks, should be fixed now on the emacs-29 branch.