update code of conduct link

https://github.com/search?q=repo%3Acarpentries%2Ftrainer-training%20https%3A%2F%2Fdocs.carpentries.org%2Ftopic_folders%2Fpolicies%2Fcode-of-conduct.html&type=code

https://docs.carpentries.org/topic_folders/policies/code-of-conduct.html
->
https://docs.carpentries.org/policies/coc/

e.g.
https://github.com/carpentries/workbench-template-rmd/commit/3bea1cbd8df2eda650e0d687aed08421f892c1ee

Start with the repository search linked in the issue to locate uses of the old Code of Conduct URL. Replace those links with https://docs.carpentries.org/policies/coc/ and verify that the outdated URL no longer appears in the repository.

Written by the indexing model from the issue text.