df.groupby on a column with complex numbers is broken
Currently, grouping by a key that has complex numbers is broken, see the following example

```python
import pandas as pd
df = pd.DataFrame([dict(a=1, b=1 + 1j), dict(a=1, b=1 + 2j)])
df.groupby("b").groups
```
output:
```
{1.0: Int64Index([0, 1], dtype='int64')}
```

expected:
```
{0: Int64Index([0], dtype='int64'), 1: Int64Index([1], dtype='int64')}
```

Related https://github.com/pandas-dev/pandas/issues/10921