CHANGELOG: Bump links for release.

Author: laurensvalk

CHANGELOG.md

@@ -828,7 +828,8 @@ Prerelease changes are documented at [support#48].
 
 
 <!-- diff links for headers -->
-[Unreleased]: https://github.com/pybricks/pybricks-micropython/compare/v3.4.0b3...HEAD
+[Unreleased]: https://github.com/pybricks/pybricks-micropython/compare/v3.4.0...HEAD
+[3.4.0]: https://github.com/pybricks/pybricks-micropython/compare/v3.4.0b3...v3.4.0
 [3.4.0b3]: https://github.com/pybricks/pybricks-micropython/compare/v3.4.0b2...v3.4.0b3
 [3.4.0b2]: https://github.com/pybricks/pybricks-micropython/compare/v3.4.0b1...v3.4.0b2
 [3.4.0b1]: https://github.com/pybricks/pybricks-micropython/compare/v3.3.0...v3.4.0b1