Conditional and required checks don't mix well on GitHub -- if a required check is skipped it still hangs, preventing PRs from getting merged indefinitely. Instead, we need to to run the action on every PR, but bail early if no docs content changes were made.
Since the logic for when/how this action runs is getting a bit convoluted, I also split up the tests against master (run against all files, no conditional checks) from the tests aginst PRs (run against changed files, with conditional checks)
9080f8e32a