bug#58992: 28.2; "lax space matching" no longer works

[Gregory Heytings]

> Hmm...

Okay, this is because of:

commit 74d091a0a665da5dc01989d1b06a61ee21b975b2
Author: Lars Ingebrigtsen <larsi@gnus.org>
Date:   Fri Sep 10 12:27:28 2021 +0200

    Change the default value of search-whitespace-regexp

    * lisp/isearch.el (search-whitespace-regexp): Change the default
    to always exclude newlines from the set (bug#21278).  It used to
    be mode-dependent whether newlines were included or not, and this
    was confusing as a user interface.

which changed the default value of search-whitespace-regexp from "\\s-+" 
to "[ \t]".