Only emit B019 when maxsize is None in lru_cache?

[lafrech]

Shouldn't B019 be emitted only when maxsize is None, as in pylint-dev/pylint#6181?

[JelleZijlstra]

Not sure about this. With a bounded size it's true that the memory leak is bounded, but it's still true that you can leak a reference to a (potentially big) object this way.