devel/py-icalendar: Update to 3.9.1

• Update PORTVERSION and distinfo checksum (3.9.1) [1]

While I'm here:

• Add USE_PYTHON=concurrent support, deprecate DOCSDIR accordingly
• Add test target and patch setup.py to support test command
• Update pkg-descr WWW URL to match setup.py:url= field

Changes:

https://github.com/collective/icalendar/blob/3.9.1/CHANGES.rst

PR: 204935
Submitted by: maintainer <jun-g daemonfreaks com> [1]