Groupby Agg not working if different partials with same name on the same column
related to #28426  from PR #28428 

from functools import partial

import pandas as pd
import numpy as np

quant50 = partial(np.percentile, q=50)
quant70 = partial(np.percentile, q=70)

test = pd.DataFrame({'col1': ['a', 'a', 'b', 'b', 'b'], 'col2': [1,2,3,4,5]})
test.groupby('col1').agg({'col2': [quant50, quant70]})

However, quant50 result is rewritten by quant70, so will get the same output on both columns.

output:

| col1  |  percentile | percentile  |
|---|---|---|
|  a | 1.7  |  1.7 |
|  b | 4.4  |  4.4 |

expected output:

| col1  |  percentile | percentile  |
|---|---|---|
|  a | 1.5  |  1.7 |
|  b | 4.0  |  4.4 |
