py-jupyter_server: updated to 2.12.3

2.12.3

Bugs fixed

- Import User unconditionally

Maintenance and upkeep improvements

- Simplify the jupytext downstream test
- Fix test param for pytest-xdist

2.12.2

Bugs fixed

- Fix a typo in error message
- Force legacy ws subprotocol when using gateway

Maintenance and upkeep improvements

- Update pre-commit deps
- Use ruff docstring-code-format

Documentation improvements

- Enable htmlzip and epub on readthedocs

(adam)