bug#62847: 29.0.90; Propertized space in Org Agenda's mode-name

[Eli Zaretskii]

> From: Ihor Radchenko <yantar92@posteo.net>
> Cc: Eli Zaretskii <eliz@gnu.org>, Stefan Monnier <monnier@iro.umontreal.ca>,
>  gusbrs.2016@gmail.com, 62847@debbugs.gnu.org
> Date: Sun, 16 Apr 2023 12:17:31 +0000
> 
> Side note: It might be interesting to have something similar to
> `add-variable-watcher' and `debug-on-variable-change', but for mutable
> objects being modified.

Propertizing a string doesn't mutate the string itself, though.