Docs pre-check never works because of 429 errors

[feywind]

GitHub changed their quota limits for loading files by non-logged-in bots, and now linkinator basically never works. Most of our other repos have stopped running it as a PR pre-check, so I want to do the same here and make the red/green work, as well as automerge.

Edit: We just need to update linkinator at some point when versions are compatible.