BUG: resample('MS') may introduce trailing empty windows

[MarcoGorelli]

Pandas version checks

• I have checked that this issue has not already been reported.

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

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

In [4]: s = pd.Series([1, 2, 3, 4, 5, 6], index=pd.date_range('2023-09-26', periods=6, freq='MS'))

In [5]: s
Out[5]:
2023-10-01    1
2023-11-01    2
2023-12-01    3
2024-01-01    4
2024-02-01    5
2024-03-01    6
Freq: MS, dtype: int64

In [6]: s.resample('MS', closed='right', label='right').mean()
Out[6]:
2023-10-01    1.0
2023-11-01    2.0
2023-12-01    3.0
2024-01-01    4.0
2024-02-01    5.0
2024-03-01    6.0
2024-04-01    NaN
Freq: MS, dtype: float64

Issue Description

not sure there's any reason for that empty bucket to be there at the end

Expected Behavior

In [6]: s.resample('MS', closed='right', label='right').mean()
Out[6]:
2023-10-01 1.0
2023-11-01 2.0
2023-12-01 3.0
2024-01-01 4.0
2024-02-01 5.0
2024-03-01 6.0
Freq: MS, dtype: float64

Installed Versions

INSTALLED VERSIONS

commit : e86ed37
python : 3.10.12.final.0
python-bits : 64
OS : Linux
OS-release : 5.10.102.1-microsoft-standard-WSL2
Version : #1 SMP Wed Mar 2 00:30:59 UTC 2022
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_GB.UTF-8
LOCALE : en_GB.UTF-8

pandas : 2.1.1
numpy : 1.25.1
pytz : 2023.3
dateutil : 2.8.2
setuptools : 67.6.1
pip : 23.1.2
Cython : None
pytest : 7.3.1
hypothesis : 6.82.4
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.2
IPython : 8.13.2
pandas_datareader : None
bs4 : 4.12.2
bottleneck : None
dataframe-api-compat: None
fastparquet : 2023.7.0
fsspec : 2023.6.0
gcsfs : None
matplotlib : 3.7.1
numba : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 12.0.1
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.11.0
sqlalchemy : 2.0.20
tables : None
tabulate : None
xarray : None
xlrd : None
zstandard : None
tzdata : 2023.3
qtpy : None
pyqt5 : None
None