KAFKA-18391 Skip running "Flaky Test Report" job on forks

[Wadimz]

Resolves KAFKA-18391

Skip running "Flaky Test Report" job on forks

Prevents jobs that fail outside main repository to be run on forks

Testing with changes applied:

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[github-actions]

A label of 'needs-attention' was automatically added to this PR in order to raise the
attention of the committers. Once this issue has been triaged, the triage label
should be removed to prevent this automation from happening again.

[github-actions]

A label of 'needs-attention' was automatically added to this PR in order to raise the
attention of the committers. Once this issue has been triaged, the triage label
should be removed to prevent this automation from happening again.

[mumrah]

Thanks for the fix! LGTM