test: fix type hinting on test_jujuversion tests

[tonyandrewmeyer]

JujuVersion's comparisons can be done against strings as well as other JujuVersions, so the type hints should reflect that.

For mocking the os.environ response, the type is dict(str, str) but I think to declare that we would need to define the dict, e.g:

    _mockenv : typing.Dict[str, str] = {}
    @unittest.mock.patch("os.environ", new=_mockenv)

And that looks considerably messier to my eyes and doesn't seem to really add value (so I've ignored the warning).

Partially addresses #1007

[benhoyt]

LGTM. Agreed the typing for patch/new is messy! new={'': ''} is shorter but confusing. So I think type: ignore is reasonable here.

Let's just do the thing I mentioned in the other PR about adding the files to pyproject.toml as we go so that's up to date. When we finish, we can replace the individual names with test/*.py.

Maybe break include onto multiple lines to avoid so many conflicts.