[Denvercoder9]

Rails isn't considered GPL because of this dependency. It is in violation of the GPL¹, which is copyright infringement. Releasing the violating software under the GPL is one way to stop that infringement, but that's not an automatic legal mechanism.

If a copyright owner decides to pursue a GPL violation, they could get damages² and enforce that the infringement stops (i.e. cease using the GPL-licensed software). It's incredibly unlikely any judge would force anybody to release source code.

¹ Actually, Rails itself isn't even in violation, because the project satisfies all the obligations the GPL imposes. GitHub would be in violation.

² In this case, where infringement wasn't intentional, they'd probably get almost nothing provided that the defendant stopped infringing when they learned of it.