[FTR] Fixup code owners check script

[wayneseymour]

Summary

Ensure paths with empty owner annotations are included in the scripts output for missing code owners

Notes

With this change, the output of the script goes from this:

succ All test files have a code owner (checked 8243 test files in 6.78 s)

to this:

...
       - x-pack/test_serverless/functional/test_suites/security/cypress/tasks/navigation.ts
       - x-pack/test_serverless/functional/test_suites/security/index.feature_flags.ts
       - x-pack/test_serverless/functional/test_suites/security/index.ts
       - x-pack/test_serverless/functional/test_suites/security/screenshot_creation/index.ts
       - x-pack/test_serverless/kibana.jsonc
       - x-pack/test_serverless/tsconfig.json
ERROR Found 2594 test files without code owner (checked 8243 test files in 7.48 s)

Eventually, this script will be included in checks on ci, such that when it returns an error, the checks will fail and report back to a given PR owner.

[elasticmachine]

Pinging @elastic/appex-qa (Team:QA)

[pheyos]

LGTM

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 395e9a2

Failed CI Steps

Metrics [docs]

✅ unchanged

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @wayneseymour