ci: Move GitHub Actions and ReadTheDocs to Python 3.14.

Python 3.14 in use by default in latest distribution releases like
Ubuntu 26.04 and Fedora 44+.

Acked-by: Eelco Chaudron <echaudron@ovn.org>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

Author: igsilya

.github/workflows/build-and-test.yml

@@ -3,7 +3,7 @@ name: Build and Test
 on: [push, pull_request]
 
 env:
-  python_default: 3.12
+  python_default: 3.14
 
 jobs:
   build-dpdk:

.readthedocs.yaml

@@ -9,7 +9,7 @@ version: 2
 build:
   os: ubuntu-26.04
   tools:
-    python: "3.12"
+    python: "3.14"
 
 # Build documentation in the "Documentation/" directory with Sphinx.
 sphinx: