BUG: Pandas named aggregation not working with resample agg

[MarcoGorelli]

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• I have confirmed this bug exists on the latest version of pandas.

• (optional) I have confirmed this bug exists on the master branch of pandas.

---

Note: Please read this guide detailing how to provide the necessary information for us to reproduce your bug.

Code Sample, a copy-pastable example

import pandas as pd

df = pd.DataFrame(
    {"group": ["a"], "col": [1.0]}, index=[pd.to_datetime("2019-11-04 10:32:09.737")]
)
df.groupby("group").resample("1D").agg(open=pd.NamedAgg("col", "first"))

Problem description

This returns

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-6-34479fc13c88> in <module>
----> 1 df.groupby('group').resample('1D').agg(open=pd.NamedAgg("col", "first"))

TypeError: aggregate() missing 1 required positional argument: 'func'

Expected Output

I think this would be

                 group  open
group                       
a     2019-11-04     a   1.0

Output of pd.show_versions()

INSTALLED VERSIONS ------------------ commit : 3ed7dff python : 3.8.2.final.0 python-bits : 64 OS : Linux OS-release : 5.3.0-51-generic Version : #44~18.04.2-Ubuntu SMP Thu Apr 23 14:27:18 UTC 2020 machine : x86_64 processor : x86_64 byteorder : little LC_ALL : None LANG : en_GB.UTF-8 LOCALE : en_GB.UTF-8

pandas : 1.1.0.dev0+1502.g3ed7dff48
numpy : 1.18.1
pytz : 2019.3
dateutil : 2.8.1
pip : 20.0.2
setuptools : 46.1.3.post20200325
Cython : 0.29.16
pytest : 5.4.1
hypothesis : 5.8.0
sphinx : 3.0.0
blosc : None
feather : None
xlsxwriter : 1.2.8
lxml.etree : 4.5.0
html5lib : 1.0.1
pymysql : None
psycopg2 : None
jinja2 : 2.11.1
IPython : 7.13.0
pandas_datareader: None
bs4 : 4.9.0
bottleneck : 1.3.2
fastparquet : 0.3.3
gcsfs : None
matplotlib : 3.2.1
numexpr : 2.7.1
odfpy : None
openpyxl : 3.0.3
pandas_gbq : None
pyarrow : 0.16.0
pytables : None
pyxlsb : None
s3fs : 0.4.2
scipy : 1.4.1
sqlalchemy : 1.3.16
tables : 3.6.1
tabulate : 0.8.7
xarray : 0.15.1
xlrd : 1.2.0
xlwt : 1.3.0
numba : 0.48.0

[MarcoGorelli]

duplicate of #32803