gh-93573: Replace wrong example domains in configparser doc (GH-93574)

* Replace bitbucket.org domain by forge.example
* Update example to python.org
* Use explicitly invalid domain

topsecret.server.com domain is not controled by PSF. It's replaced by invalid topsecret.server.example domain. It follows RFC 2606, which advise .example as TLD for documentation.
(cherry picked from commit 924a3bfa28578802eb9ca77a66fb5d4762a62f14)

Co-authored-by: sblondon <stephane.blondon@gmail.com>