B033 should say what the duplicate set item is

[JelleZijlstra]

I got an error taxonomy/parsing.py:87:11: B033 Sets should not contain duplicate items. Duplicate items will be replaced with a single item at runtime.

Now, part of this set looks like this:

            "İ",
            "À",
            "Á",
            "Ć",
            "Á",
            "Å",
            "Ä",

I think it's the Á, but it would have been more helpful if flake8-bugbear had told me directly.

I'll work on a fix.