From the man ( Guillaume Laforge) himself:

As I said on my blog, and as is said on the FAQ, the license of Groovy
will stay Apache 2.
No worries to have there.

To make a parallel, it’s not because SpringSource acquired Covalent
(the main Tomcat committers) that they made Tomcat change its license.
Same goes with Groovy: Groovy will stick to ASL 2.