s/tails.boum.org/tails.net

[rocodes]

Describe the change

https://tails.boum.org now redirects to https://tails.net (yay) so let's update the docs

https://tails.net/news/new_domain/index.en.html

https://gitlab.tails.boum.org/tails/tails/sysadmin/-/issues/17985/