BUG: Fix to GH34422 SeriesGroupBy works only with 'func' now
- [X] closes #34422 
- [x] tests added / passed
- [x] passes `black pandas`
- [x] whatsnew entry

This PR tries to fix the bug pointed in #34422 where `SeriesGroupBy.agg` works with any given column name in `NamedAgg`.

After discussing with @TomAugspurger  and @MarcoGorelli  in another issue #34380 regarding this issue in the comments, We came to a solution that

> So for SeriesGroupBy.agg, if there are any tuples or NamedAgg present in kwargs then I think we should raise.
> Disallowing `NamedAgg` and tuples with `SeriesGroupBy`.

#### Before fix:
```python3
s = pd.Series([1,1,2,2,3,3,4,5])
s.groupby(s.values).agg(one = pd.NamedAgg(column='anything',aggfunc='sum'))
  one
1    2
2    4
3    6
4    4
5    5

s.groupby(s.values).agg(one=('something','sum'))
   one
1    2
2    4
3    6
4    4
5    5
```

#### After fix:
```python3
s = pd.Series([1,1,2,2,3,3,4,5])
s.groupby(s.values).agg(one = pd.NamedAgg(column='anything',aggfunc='sum'))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "d:\#gh34422\pandas\pandas\core\groupby\generic.py", line 243, in aggregate
    raise TypeError(tuple_given_message.format(type(kwargs[col]).__name__))
TypeError: 'func' is expected but recieved NamedAgg in **kwargs.

s.groupby(s.values).agg(one=('something','sum'))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "d:\#gh34422\pandas\pandas\core\groupby\generic.py", line 243, in aggregate
    raise TypeError(tuple_given_message.format(type(kwargs[col]).__name__))
TypeError: 'func' is expected but recieved tuple in **kwargs.
```