tests(helpers): separate grpc test functions

[chronolaw]

Summary

KAG-5242

Checklist

• [ ] The Pull Request has tests
• [x] A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• [ ] There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

Fix #[issue number]