devel/py-pip: Reenable DOCS option by using py-towncrier23

• Bump PORTREVISION for package change

Change py-sphinxcontrib-towncrier and this port from incompatible py-towncrier
to compatible py-towncrier23. Therefore, DOCS can be enabled again.

Reference: https://github.com/sphinx-contrib/sphinxcontrib-towncrier/issues/92
PR: 280570