Clear your .gradle system cache and try again. It’s not using GTNH2’s repository, it’s using normal forge, and they broke their server last year, I’m guessing your cache predates that so you are just using your cached version of their services.
And check the git repo on github, the ./gradlew is not marked as executable, lol.
EDIT: Also promoted your user here so you can use non-whitelisted links.