len8 doesn't run on Python 3.8

[Jonxslays]

Describe the bug

len8 does not appear to run properly on python 3.8, I have not tested on versions lower than that. I'm not 100% sure if this is a usage issue on our end, or something else.

The error is as follows:

nox > len8 -l yami tests
Traceback (most recent call last):
  File "/home/runner/work/Yami/Yami/.nox/formatting/bin/len8", line 8, in <module>
    sys.exit(main())
  File "/home/runner/work/Yami/Yami/.nox/formatting/lib/python3.8/site-packages/len8/__main__.py", line 44, in main
    checker.check(*parser.paths)
  File "/home/runner/work/Yami/Yami/.nox/formatting/lib/python3.8/site-packages/len8/models/checker.py", line 210, in check
    self._check_dir(p)
  File "/home/runner/work/Yami/Yami/.nox/formatting/lib/python3.8/site-packages/len8/models/checker.py", line 145, in _check_dir
    self._check_file(p)
  File "/home/runner/work/Yami/Yami/.nox/formatting/lib/python3.8/site-packages/len8/models/checker.py", line 140, in _check_file
    if self._is_valid(path):
  File "/home/runner/work/Yami/Yami/.nox/formatting/lib/python3.8/site-packages/len8/models/checker.py", line 134, in _is_valid
    if path.is_relative_to(e):
AttributeError: 'PosixPath' object has no attribute 'is_relative_to'
nox > Command len8 -l yami tests failed with exit code 1

To Reproduce

Using python 3.8:

pip install len8
len8 .

Expected behavior

len8 will run successfully, but it does not.

System Information:

• OS:
  • Ubuntu 20.04.3 LTS
  • Mac OS X 10.15.7
  • Windows server 2019 10.0.17763
• Python Version: 3.8.12
• len8 Version: 0.4.0

Additional context
It appears this is specifically related to the changes we made to the filter to use Path.is_relative_to.
A link to my failed CI run can be found here.