The new libxml2 2.15.0 breaks the compilation of in-tree documentation

Hello,

the newly released libxml2 2.15.0 errors out when it finds a trailing space in
the value of an attribute. This was not an error before (thanks to arojas for
reporting this).

Namely, stuff like

<ulink url=" https://kde.org">...
and
<ulink url="https://kde.org ">...

now produce an error like:

"validity error : standalone: normalization of attribute url on ulink by
external subset declaration"

The reason is
https://gitlab.gnome.org/GNOME/libxml2/-/commit/e4cbc295fa97f3c290cec8b243bd96ebdaa3dab2
namely:

You may see this in in packages with documentation during the compilation of
the documentation.

I think I've fixed all occurrences of the issue both in the sources where it
happened and in the translations. I may have missed some though. Translators,
please find out if you see more, and if you have an idea on how to add
automated checks to prevent broken documentation from being added, I'm all ears.

About the impact on the repositories:
- Frameworks: not affected (apart from an error in the 5.x branch of kjsembed,
which I hope no one cares about anymore)
- Plasma: fixed in the upcoming 6.5.0.
- Gear: fixed in the upcoming 25.08.2

A few other applications outside the ones listed above are affected - I admit
I lost track of the changes. A new release may be needed for those, but please
let us (translation coordinators) know if you hit such issues.

If you need to compile something, right now just remove the affected docbook
files (translated or not) before compiling the package.

-- 
Luigi