.readthedocs.yml: update Python version and Ubuntu release

The current documentation build dependencies are not compatible with
Python 3.9. Update to Python 3.12.

Use the current Ubuntu LTS release, i.e. 24.04 Noble Numbat.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
1 file changed