devel/py-pytest-xdist: Update to 1.13.1

• Update PORTVERSION and distinfo checksum (1.13.1)
• Match COMMENT to setup.py:description
• Enable 'concurrent' Python support
• Add NO_ARCH
• Update test target to new conventions
• Remove pycache from WRKSRC/testing
• Update pkg-descr WWW: URL to match next version and new repo URL

Changes:

https://github.com/pytest-dev/pytest-xdist/blob/v1.13.1/CHANGELOG