sysutils/py-ansible-lint: upgrade to 6.0.2
Clarify the license: this software has always been released under
GPLv3, but GitHub auto-labelled it as MIT licensed due to the presence
of LICENSE.txt. While it uses some MIT licensed modules, it is GLPv3
licensed itself.
Make py-yamllint a required dependency rather than something it would
optionally use if present on the system.