[LTP] [PATCH 1/4] readthedocs: Update to Ubuntu 26.04, Sphinx 8.2.3

[Petr Vorel]

Update readthedocs.org environment + local requirements.txt
* Ubuntu 24.04 => 26.04
* Sphinx 7.2.6 => 8.2.3 (based on Ubuntu 26.04 version to match local
  development with readthedocs.org)
* sphinx-rtd-theme 2.0.0 => 3.1.0 (required by Sphinx 8.2.3 update)

This helps to use newer Sphinx features.

Signed-off-by: Petr Vorel <pvorel@suse.cz>
---
 .readthedocs.yml     | 2 +-
 doc/requirements.txt | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/.readthedocs.yml b/.readthedocs.yml
index 51825da77f..bb70bce70d 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -1,7 +1,7 @@
 version: 2
 
 build:
-  os: "ubuntu-24.04"
+  os: "ubuntu-26.04"
   tools:
     python: "3.12"
   apt_packages:
diff --git a/doc/requirements.txt b/doc/requirements.txt
index 442ff2eee6..f04676c7bd 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,7 +1,7 @@
 # Use the same sphinx as on readthedocs.org. When updated, make sure
 # sphinx-rtd-theme is compatible with sphinx.
-sphinx==7.2.6
-sphinx-rtd-theme==2.0.0
+sphinx==8.2.3
+sphinx-rtd-theme==3.1.0
 
 linuxdoc==20240924
 sphinxcontrib-spelling==7.7.0
-- 
2.55.0