Fix LICENSE link to use full GitHub URL for consistency

Co-authored-by: rrobetti <7221783+rrobetti@users.noreply.github.com>

Author: Copilot

CONTRIBUTING.md

@@ -410,7 +410,7 @@ We're here to help! Don't hesitate to ask questions.
 
 ## License
 
-By contributing to OJP, you agree that your contributions will be licensed under the [Apache License 2.0](LICENSE).
+By contributing to OJP, you agree that your contributions will be licensed under the [Apache License 2.0](https://github.com/Open-J-Proxy/ojp/blob/main/LICENSE).
 
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