Follow-up to #468.

In a GitHub Enterprise Server (GHES) environment where GitHub Connect is not enabled (i.e. actions are shipped-in box with the appliance, and not downloaded from GitHub.com) the actions/upload-artifact@v3-node20 and actions/download-artifact@v3-node20 branches/tags/references do not exist in the actions repositories that ship with the appliance.

Accordingly, it is not possible to use actionlint v1.7.4+ in GHES as it is impossible to upgrade from v3 to v4 as it is not supported. I assume GHES doesn't enforce the Node.js v16 restriction internally in GHES environments as they are still functional.

My suggestion for a fix would be to not issue these warnings if the GITHUB_SERVER_URL environment variable is not https://github.com and does not end with .ghe.com (for GitHub Enterprise Cloud) (docs).