Fix Read the Docs bulid failing

[ciscorn]

This PR will fix the following errors:

• https://readthedocs.org/projects/circuitpython/builds/11605442/

    File "tools/extract_pyi.py", line 91, in convert_folder
      filenames = sorted(os.listdir(top_level))
  FileNotFoundError: [Errno 2] No such file or directory: 'extmod/ulab/code'
  

• https://readthedocs.org/projects/circuitpython/builds/11616854/

    File "tools/extract_pyi.py", line 48, in find_stub_issues
      for arg_node in (node.args + node.posonlyargs + node.kwonlyargs):
  AttributeError: 'arguments' object has no attribute 'posonlyargs'
  

[jepler]

Is the change to the ulab submodule itself intended? Are these changes merged into ulab?

[ciscorn]

@jepler
Not intended, but it is the HEAD of ulab's origin/master that has the latest stubs. So it should be ok.

[ciscorn]

The CI failed with the latest ulab stubs. It seems we have to wait for autoapi to support the @overload decorator. (readthedocs/sphinx-autoapi#239).

For now, I reverted the update of the ulab submodule to make this PR pass the test.

[jepler]

Thanks!