Ensure that all imports are listed in dependencies

[krassowski]

It would have caught #83

[krassowski]

Hmm we are already running a reasonable matrix:

[krassowski]

I suppose #83 was not caught because tomli was already a dependency of another package and did not need to be explicitly installed on CI.

jupyter-builder/jupyter_builder/federated_extensions.py

Lines 29 to 32 in a140a88

	try:
	from tomllib import load # Python 3.11+
	except ImportError:
	from tomli import load

Maybe we should use https://github.com/osprey-oss/deptry (here and elsewhere)?