dns/py-pycares: Update to 2.3.0

Changelog:
https://github.com/saghul/pycares/blob/pycares-2.3.0/ChangeLog

• Set LICENSE_FILE.
• Define the do-test target.
• Strip _core.so.

PR: 234452
Reviewed by: krion@
Approved by: demon@ (maintainer), krion@ (mentor)
Differential Revision: https://reviews.freebsd.org/D18671