bug#45581: 28.0.50; C-M-v in xref buffers shows a different buffer when scrolling

[Daniel Martín]

Steps to reproduce the problem:

1. emacs -Q
2. Open any file with source code (for example, xdisp.c).
3. Place the point in any symbol (for example, redisplay_internal).
4. Press M-? (`xref-find-references').
5. In the *xref* buffer, press n (`xref-next-line').
6. Press C-h m (`describe-mode').
7. Press C-M-v to scroll the help window.

Expected results:

The mode description window scrolls as usual.

Actual results:

The buffer with the file that contains the selected xref item replaces
the *Help* buffer and is scrolled instead.

I can't reproduce the same behavior in *grep* buffers.