[Ops] skip flaky custom_fields tests

[delanni]

Summary

Skips flaky suite: #176805

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 6d4ed08

Failed CI Steps

• FTR Configs #28
• FTR Configs #96

Test Failures

• [job] [logs] FTR Configs #28 / discover/group1 discover test query #2, which has an empty time range should show matches when time range is expanded
• [job] [logs] FTR Configs #96 / discover/group1 discover test query #2, which has an empty time range should show matches when time range is expanded

Metrics [docs]

✅ unchanged

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