net-mgmt/py-ncclient: Update to 0.6.2.

• Add conditional RUN_DEPENDS on devel/py-selectors2.

PR: 230874
Submitted by: John W. O'Brien <john@saltant.com>
Reviewed by: Sergey Akhmatov <sergey@akhmatov.ru> (maintainer)
Reviewed by: tobik (previous version)
Reviewed by: wen
Approved by: mat (mentor)
Approved by: Sergey Akhmatov <sergey@akhmatov.ru> (maintainer)
Differential Revision: https://reviews.freebsd.org/D17231