python/go environments.yaml compatibility

[roger peppe]

I was looking to resolve this ticket on our kanban board:

"Right now, py-juju will let you have keys that it doesn't understand,
but juju-core will fail to start if there are any unrecognized keys.

The best compromise seemed to be having juju-core do strict parsing on
the selected environment (--environment/-e), but to ignore the
contents of other environments."

AFAICS the assertion in the first paragraph is not true.  Current the
Go juju command will fail to start only if there are unrecognized keys
*in the selected environment*. This seems exactly like the compromise
suggested in the second paragraph, so I am thinking of abandoning
the ticket.

However I feel I may be missing something here. Anyone?