That's fairly reasonable. At least they can prompt you "Did you really mean to do this?" -- they have enough infrastructure to update your project page with a "Make pull request" button after you push, they can repurpose that for a "Approve next push without asking questions."

Alternatively, if they supported custom pre-receive hooks via e.g. webhooks, someone could publish a script or stand up a web server to check for such things.

Supporting git hooks on github would be really great. Always wanted to have them for rejecting debug statements, or as a rudimentary poor-man's-ci / linter