[sdk-platform-java] [Policy Bot] found one or more issues with this repository.

[Policy Bot](https://github.com/googleapis/repo-automation-bots/tree/main/packages/policy#policy-bot) found one or more issues with this repository.
- [x] Default branch is 'main'
- [x] Branch protection is enabled
- [x] Merge commits disabled
- [ ] There is a CODEOWNERS file
- [x] GitHub [detects a valid LICENSE.md](https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/licensing-a-repository#detecting-a-license)
- [x] There is a CODE_OF_CONDUCT.md
- [x] There is a CONTRIBUTING.md
- [x] There is a SECURITY.md