Update copyright dates to 2023, and license to GPL3
The licence for Sympl 11 should be updated to the more modern GPL3, which is a bit clearer in a few cases.
Similarly, copyright dates should also be updated.
The 17.0 major release is coming on May 16, 2024! This version brings many exciting improvements to GitLab, but also removes some deprecated features. We are introducing three breaking change windows during which we expect breaking changes to be deployed to GitLab.com. You can read more about it on our blogpost. The first breaking change window begins 2024-04-22 09:00UTC and ends 2024-04-24 22:00UTC.
The licence for Sympl 11 should be updated to the more modern GPL3, which is a bit clearer in a few cases.
Similarly, copyright dates should also be updated.