BUG: Categorical of booleans has object .categories

[ivirshup]

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 [1]: import pandas as pd
   ...: 
   ...: obs = pd.DataFrame({"int_cat":[1,2,3], "bool_cat":[True,False,False]}, dtype="category")
   ...: obs["bool_cat"].cat.categories.dtype
Out[1]: dtype('O')

In [2]: bools = pd.Series([True, False, True])
   ...: bools.dtype
Out[2]: dtype('bool')

In [3]: bools.astype("category").cat.categories.dtype
Out[3]: dtype('O')

In [4]: pd.__version__
Out[4]: '1.4.1'

Issue Description

I would assume a categorical generated from a boolean array would have bool category values, not object.

This is weird, but it's admittedly a funny use case. Upstream of scverse/anndata#724

Expected Behavior

I would have expected the dtype of the categories to be boolean.

Installed Versions

``` ------------------ commit : 06d2301 python : 3.9.10.final.0 python-bits : 64 OS : Darwin OS-release : 20.6.0 Version : Darwin Kernel Version 20.6.0: Wed Nov 10 22:23:07 PST 2021; root:xnu-7195.141.14~1/RELEASE_X86_64 machine : x86_64 processor : i386 byteorder : little LC_ALL : None LANG : None LOCALE : None.UTF-8

pandas : 1.4.1
numpy : 1.21.5
pytz : 2021.3
dateutil : 2.8.2
pip : 22.0.3
setuptools : 60.5.0
Cython : 0.29.25
pytest : 7.0.1
hypothesis : None
sphinx : 4.1.2
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.0.3
IPython : 8.1.0
pandas_datareader: None
bs4 : None
bottleneck : None
fastparquet : None
fsspec : 2022.02.0
gcsfs : None
matplotlib : 3.5.1
numba : 0.55.1
numexpr : 2.8.1
odfpy : None
openpyxl : 3.0.9
pandas_gbq : None
pyarrow : 7.0.0
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.8.0
sqlalchemy : 1.4.31
tables : 3.7.0
tabulate : 0.8.9
xarray : 0.21.1
xlrd : 1.2.0
xlwt : None
zstandard : None

</details>

[phofl]

This is fixed on main.

May need tests

[rxd330]

Hi, I am new to open-source community and would like to work on this.

[rxd330]

take

[matiasarebalo]

Hi my name is matias, im from argentina, im new to open-source community and would like to try it. so tell me if i can help you with this.

[rxd330]

Hi my name is matias, im from argentina, im new to open-source community and would like to try it. so tell me if i can help you with this.

Hi, thanks for offering help. At this time, I don't need your help. I will let you know when there's something up. Thanks again.

[Kyrpel]

Hi my name is matias, im from argentina, im new to open-source community and would like to try it. so tell me if i can help you with this.

Hi Matias. If you find an issue that interests you, just write in the comments "take" and the issue will be assigned to you, so other contributors know about it. If you want to drop the issue just press "unassign me" at the right of the issue description