jsonschema deprecation warning

Running the tests using jsonschema version 4.19.2, I received the following warning:

../../../../../usr/lib/python3/dist-packages/sphinxcontrib/openapi/utils.py:27
  /usr/lib/python3/dist-packages/sphinxcontrib/openapi/utils.py:27: DeprecationWarning:
  jsonschema.RefResolver is deprecated as of v4.18.0, in favor of the
  https://github.com/python-jsonschema/referencing library, which provides more compliant
  referencing behavior as well as more flexible APIs for customization. A future release will remove
  RefResolver. Please file a feature request (on referencing) if you are missing an API for the kind
  of customization you need.
    class OpenApiRefResolver(jsonschema.RefResolver):

So utils.py should be updated at some point, probably in the not-too-distant future.

[EDIT: manually wrapped the long warning message to avoid having to scroll as far]

Start with sphinxcontrib/openapi/utils.py at the OpenApiRefResolver definition and review the jsonschema deprecation warning for the referencing replacement. Run the project tests with jsonschema 4.19.2 and confirm the warning is no longer emitted while the OpenAPI extension remains functional.