BUG: groupby.agg fails when input has duplicate columns and dict input

[rhshadrach]

df = DataFrame(
    [[1, 2, 3, 4], [1, 3, 4, 5], [2, 4, 5, 6]],
    columns=["a", "b", "c", "c"],
)
gb = df.groupby("a")
gb.agg({"c": "sum"})

raises AttributeError: 'DataFrame' object has no attribute 'name'. Did you mean: 'rename'?

I would expect it to aggregate both of the columns named "c".

[undermyumbrella1]

Hi I have created a pr to address this ticket, may I request for some help reviewing it? thank you