Bump Python max version to 3.14 in CI

[Darshan808]

Python 3.14 has been released, so this PR updates the CI configuration to include it as the new maximum supported version.

[krassowski]

Based on logs it looks like this will require updating:

jupyterlab_server/jupyterlab_server/test_utils.py

Lines 164 to 182 in 1acc30b

	def maybe_patch_ioloop() -> None:
	"""a windows 3.8+ patch for the asyncio loop"""
	if (
	sys.platform.startswith("win")
	and tornado.version_info < (6, 1)
	and sys.version_info >= (3, 8)
	):
	try:
	from asyncio import WindowsProactorEventLoopPolicy, WindowsSelectorEventLoopPolicy
	except ImportError:
	pass
	# not affected
	else:
	from asyncio import get_event_loop_policy, set_event_loop_policy
	if type(get_event_loop_policy()) is WindowsProactorEventLoopPolicy:
	# WindowsProactorEventLoopPolicy is not compatible with tornado 6
	# fallback to the pre-3.8 default of Selector
	set_event_loop_policy(WindowsSelectorEventLoopPolicy())

[Darshan808]

Based on logs, it seems the error originates from jupyter_core_code using asyncio.WindowsSelectorEventLoopPolicy. According to the Python 3.14 deprecations, this policy has been deprecated.

[Darshan808]

I see this deprecation being tracked in jupyter/jupyter_core#445