"unused 'type: ignore' comment" should be of severity "warning" / "note"

[blueyed]

I think the "unused 'type: ignore' comment" errors should be not of type "error", but rather "note" (or "warning", but that does not exist yet really AFAICS).

While changing this to "note" would be trivial, I think it should be considered to start using a severity of "warning", and use this here then.

(This is relevant for when using mypy as a linter, where the type of "error" is relevant.
I am transforming "Need type (annotation|comment) for …" errors to "info" already for example, but that should really be reflected in mypy's output already in a better way.
Related: #6919.)

[JukkaL]

Yeah, if we had support for a 'warning' error level this would make sense. Leaving as 'needs discussion' since we haven't really considered the impliciations of adding a 'warning' error level.