[BUG] `pivot_longer` test cases failed on pandas latest (1.4.x) passed on 1.3.x

[Zeroto521]

I found why #1143 failed on pivot_longer, encode_categorical, and _select_column test cases
The core reason is the version compatibility.
Our current test environment only tests one main pandas version 1.3.x. But the latest pandas version is 1.4.x.

pyjanitor/environment-dev.yml

Line 36 in a027753

- pandas=1.3.5

There pivot_longer method test cases failed on pandas latest version (1.4.x), but passed on 1.3.x.

Call for helping @samukweku, (I do use less about pivot_longer accessor, so I can't handle these problems).

• tests/functions/test_pivot_longer.py::test_names_pattern_str
• tests/functions/test_pivot_longer.py::test_names_sep
• tests/functions/test_pivot_longer.py::test_names_transform_numeric

[samukweku]

@Zeroto521 Do you have any idea about the test_documentation_build.py failure?

[Zeroto521]

Mkdocs and its related packages are not in environment.