[LTP] readthedocs: Update to Ubuntu 26.04, Sphinx 8.2.3

[Petr Vorel]

> Hi Petr,

> On Aug 5, 2026, Petr Vorel wrote:
> > [PATCH 1/4] readthedocs: Update to Ubuntu 26.04, Sphinx 8.2.3

> --- [PATCH 2/4] ---

> > +# linuxdoc 20260504 is too verbose by default

> Could this change be folded into patch 3? At this point the requirements
> still pin linuxdoc 20240924, so the comment names a version that is not
> present in this commit, and the commit message explicitly depends on the
> following patch.

I deliberately wanted to fix it before updating linuxdoc + document the reason
even in the source code. But, if preferred, I can swap 2rd and 3nd patch.

Kind regards,
Petr