BUG: df.resample('MS', closed='right') incorrectly places bins

[MarcoGorelli]

• closes BUG: df.resample('MS', closed='right') incorrectly places bins #55271 (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

[MarcoGorelli]

I find it odd that these "*start" offsets are here to begin with, as they don't have an associated Period:

In [22]: MonthEnd()._period_dtype_code
Out[22]: 3000

In [23]: MonthBegin()._period_dtype_code
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[23], line 1
----> 1 MonthBegin()._period_dtype_code

AttributeError: 'pandas._libs.tslibs.offsets.MonthBegin' object has no attribute '_period_dtype_code'

So, trying this - let's see what fails

[MarcoGorelli]

nvm, this stuff is explicitly tested for...

pandas/pandas/tests/indexes/datetimes/methods/test_to_period.py

Lines 53 to 63 in a98be06

	@pytest.mark.parametrize("off", ["BQ", "QS", "BQS"])
	def test_to_period_quarterlyish(self, off):
	rng = date_range("01-Jan-2012", periods=8, freq=off)
	prng = rng.to_period()
	assert prng.freq == "Q-DEC"
	@pytest.mark.parametrize("off", ["BA", "AS", "BAS"])
	def test_to_period_annualish(self, off):
	rng = date_range("01-Jan-2012", periods=8, freq=off)
	prng = rng.to_period()
	assert prng.freq == "A-DEC"