Update to latest openapi-spec-validator

[bollwyvl]

Problem

There is some bad metadata in the upstreams:

• removing default_handlers breaks openapi-core python-openapi/openapi-spec-validator#173

Proposed Solution

Go ahead and update to, and only support the lastest versions of, openapi-core, openapi-spec-validator.

Additional context

• [bot-automerge] jupyterlab_server v2.16.6 conda-forge/jupyterlab_server-feedstock#83
• a pip check somewhere might help catch this, but as they are [extras]....
• py.typed is provided in the more recent versions, which should help things
• we'll likely end up with an OpenAPI wrapper for tornado, which would be virtuous to upstream, and reuse in other places