I did that and it solved the memory leaks with Bean Validation

I'd like to do that, but I can't create a pull request because there is only a master branch.

Why would that stop you from creating a pull request. In fact the pull request should be for the master branch of https://github.com/beanvalidation/beanvalidation-api. Whether you use the master branch of your fork or a dedicated feature branch on your forked repository is a different story. The general idea is to push the changes to your fork of beanvalidation-api and create the pull request from there. See also https://help.github.com/articles/creating-a-pull-request