Update CODEOWNERS (#4196)
Update CODEOWNERS (#4196)

java-samples-reviewers was left out.

- [x] Please **merge** this PR for me once it is approved.

GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples,GoogleCloudPlatform/java-docs-samples