Fix: let scroll-other-window/scroll-other-window-down work

[whatacold]

Hi,

Many people have the requirement to scroll pdf-view buffer from the other org buffer while reading PDF, to name a few:

1. https://github.com/politza/pdf-tools/issues/55
2. https://lists.gnu.org/archive/html/emacs-devel/2015-12/msg01416.html
3. https://www.reddit.com/r/emacs/comments/10pkhko/how_to_navigate_to_previousnext_pdf_page_in/

This PR makes it work, at least for Emacs 29.3.