First, the copyright notice doesn't really do much. Any copyright status, licensing, etc apply whether or not there's a notice.

Second, if you created it, you have full control on how you license it. You can even use multiple licenses. It's common to have GPL (or similar) for personal use, and commercial use being licensed separately for a fee.

If you didn't create it (other contributors did), then each contribution is owned and copyrighted by each contributor. Presumably they have licensed their works under the GPL.

Do you have a specific reason to even include a copyright notice?