Custom Github Actions workflows are disallowed

This issue is just a reminder of our custom Github Actions worfklows policy. [Quoting from the docs](https://conda-forge.org/docs/maintainer/infrastructure/#third-party-use-of-our-ci-services):

> Due to its stature in the open-source community, conda-forge has enhanced access to certain CI services. This access is a community resource entrusted to conda-forge for use in building packages. We thus cannot support third-party or "off-label" CI jobs in our feedstocks on any of our CI services. If we find such use, we will politely ask the maintainers to rectify the situation. We may take more serious actions, including archiving feedstocks or removing maintainers from the organization, if the situation cannot be rectified.