release-25.4: revert: deflake TestRevertSpansFanout under race

[kev-cao]

Backport 1/1 commits from #162474 on behalf of @kev-cao.

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This test spins up a multi-node cluster, which is flaky when under race.

Fixes: #162132

Fixes: #162193

Fixes: #161164

Release note: None

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Release justification: Test-only change.

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes. Includes test-only changes, build system changes, etc.
• Fixes for serious issues. Defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to.

Add a brief release justification to the PR description explaining your selection.

Also, confirm that the change does not break backward compatibility and complies with all aspects of the backport policy.

All backports must be reviewed by the TL and EM for the owning area.

[cockroach-teamcity]

This change is 

[blathers-crl]

✅ PR #162549 is compliant with backport policy

Confidence: high
Backward compatible: true
Explanation: The pull request is compliant with the backport policy because it contains a 'Release justification: Test-only change' in the PR body, satisfying the exception for changes that only affect non-production code. Additionally, the files changed in this PR are associated with test code. Specifically, the file pkg/revert/revert_test.go is a test file, and changes here indicate modifications to unit tests, including the use of a helper from the testutils package to skip tests when under race conditions. The modification in pkg/revert/BUILD.bazel adds a dependency related to testing utilities, which also falls within the scope of non-production, workflow-related changes.

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