BUG: isin propagates nulls for DataFrame but not Series

[brandon-b-miller]

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Reproducible Example

import pandas as pd

# dataframe with an Int64 column and a missing value
df = pd.DataFrame(
    {
        'a': pd.Series([1,2,pd.NA], dtype='Int64')
    }
)

values = pd.Series([1,2,3], dtype='Int64')

print(df.isin(values)) # [True, True, <NA>]

# equivalent series
sr = pd.Series([1,2,pd.NA], dtype='Int64')

print(sr.isin(values)) # [True, True, False]

Issue Description

The null propagation behavior for isin differs depending on if the calling object is a Series or a DataFrame, should they be the same? e.g. should the series isin call return a null in the last position?

Expected Behavior

I would expect to get a null at index 2 in both cases.

Installed Versions

INSTALLED VERSIONS

commit : 66e3805
python : 3.8.12.final.0
python-bits : 64
OS : Linux
OS-release : 4.15.0-76-generic
Version : 86-Ubuntu SMP Fri Jan 17 17:24:28 UTC 2020
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.3.5
numpy : 1.21.5
pytz : 2021.3
dateutil : 2.8.2
pip : 22.0.3
setuptools : 59.8.0
Cython : 0.29.27
pytest : 7.0.0
hypothesis : 6.36.1
sphinx : 4.4.0
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.0.3
IPython : 8.0.1
pandas_datareader: None
bs4 : 4.10.0
bottleneck : None
fsspec : 2022.01.0
fastparquet : None
gcsfs : None
matplotlib : 3.5.1
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 6.0.1
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
numba : 0.55.1

[phofl]

This was discussed in #38379 (comment)

But no definite solution I think

[phofl]

cc @jorisvandenbossche

Thoughts here?

If we don't want NA to propagate, then the Series case is wrong