Fix broken link to CoC enforcement

[JasonWeill]

Fixes a broken link from governance/conduct/code_of_conduct.md to …/enforcement.md, as first observed by @adriens in jupyterlab/jupyter-ai#577 (comment) — thanks!

[krassowski]

I don't believe the link is broken when deployed on https://jupyter.org/governance/conduct/code_of_conduct.html and would worry that it could possibly break with this change. It is just not meant to be used on GitHub - see that all other links are without .md

[JasonWeill]

I did find two links that already ended in .md:

This one is properly transformed to .html in the published docs:

governance/conduct/reporting_online.md

Line 7 in bbb9ff9

confidential. Code of Conduct reports are currently reviewed by the [Executive Council](../executive_council.md). In some cases we may determine that a public statement will need

This one is not; "standard procedure" renders as regular text, not as a link:

governance/conduct/reporting_online.md

Line 53 in bbb9ff9

[standard procedure](enforcement.md#Resolutions) to arrive at and

[JasonWeill]

Fixed the latter link above to link to a page; linking to a named anchor doesn't seem to be supported. Tested locally.

[JasonWeill]

Thank you @willingc ! I don't have write access to this repository. Would you be able to merge this change in, please?