Earlier quoted context omitted.
GitHub ToS allow terminating accounts for malicious behaviour, which I'd argue that purposefully breaking downstream code is.
Why would the developer of any software that comes explicitly without warranty be hold responsible for downstream breakages? It's not as if one could force people to upgrade to newer versions and they can always keep depending on the old releases.
Without a warranty, you're not held to strict liability, but you can probably be held liable under the default legal regime. If I buy real estate and get a quit-claim deed, there is no promise that the seller has unencumbered rights to the property. However, if I can show the seller intentionally defrauded me, they can still be held civilly and criminally liable for the fraud.