sets in str.cat?!
In #20347, I was asked to allow list-like inputs for the `.str.cat` methods for Series. However, I didn't know that `is_listlike({'a', 'b', 'c'})` is True (for sets) until I stumbled over it in #22486.

These objects should imo clearly be disallowed, lest users shoot themselves in the foot massively:
```
>>> s = pd.Series(['a', 'b', 'c'])
>>> s.str.cat({'a', 'b', 'c'})
0    ac
1    bb
2    ca
dtype: object
```

I'm not even sure this should go through a deprecation cycle - IMO it's just a plain ol' bug that should be fixed ASAP.