Audit pyproject.toml for Funding = Numfocus, and add Funding = to missing ones.

[Carreau]

See recent jupyter-server/jupyter_server#1485, Many projects are affected:

$ rg 'Funding = ' -t toml
ipykernel/pyproject.toml
42:Funding = "https://numfocus.org/donate"

traitlets/pyproject.toml
30:Funding = "https://numfocus.org"

jupyter_server/pyproject.toml
50:Funding = "https://jupyter.org/about#donate"

pytest-jupyter/pyproject.toml
60:Funding = "https://numfocus.org/donate"

ipython/pyproject.toml
54:Funding = "https://numfocus.org/"

jupyter_core/pyproject.toml
37:Funding = "https://numfocus.org/"