Adds failing test for dict buckets with 2 items

@rixner here's one reason why there can be more that on items in a bucket.

How do you sugest we differentiate between 

```py
>>> d = { 1: 5 }
>>> d[1.0] = 6
>>> d
    {1: 6}
```
eg. both leading to the same value. And the test I added here where they do have the same `__hash__` but are not the same according to the dictionary key function.