CHANGELOG: fix missing "v" in version

Author: dlech

CHANGELOG.md

@@ -19,5 +19,5 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 
 [Unreleased]: https://github.com/pybricks/pybricksdev/compare/v1.0.0-alpha.2..HEAD
-[1.0.0-alpha.2]: https://github.com/pybricks/pybricksdev/compare/v1.0.0-alpha.1...1.0.0-alpha.2
+[1.0.0-alpha.2]: https://github.com/pybricks/pybricksdev/compare/v1.0.0-alpha.1...v1.0.0-alpha.2
 [1.0.0-alpha.1]: https://github.com/pybricks/pybricksdev/compare/v1.0.0-alpha.0...v1.0.0-alpha.1