even if you
were infringing on Valve's copyrights (which you probably aren't, you're just using one of their trademarks), licensing your project or not wouldn't change that at all. but more importantly, by not including a license file in your repository, you are asking everyone to assume that your project is not licensed, therefore all rights are reserved, therefore it's not actually open-source (a comment on HN is sadly not enough):
https://docs.github.com/en/repositories/managing-your-reposi....