9.2.4 release web module import errors

!9727 (merged) introduced a new file to the web module: Web/Python/vtkmodules/web/errors.py

This file appears not to be shipping in the distribution. Causing a failed import:

>>> from vtkmodules.web.protocols import *
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/miniconda3/envs/pyvista-dev/lib/python3.9/site-packages/vtkmodules/web/protocols.py", line 12, in <module>
    from vtkmodules.web.errors import WebDependencyMissingError
ModuleNotFoundError: No module named 'vtkmodules.web.errors'
>>>

When I inspected the files installed from the wheel, indeed the errors.py file was missing. This is quite odd. Did we forget to add the file to a manifest or something?

cc @ben.boeckel @sebastien.jourdain