Remove unsourced flaky test failure statistic

[samgutentag]

Summary

• Replaces the unsourced "20-40% of PR failures" claim on the anti-flake protection page with qualitative language
• Flagged by Matt Matheson in Slack thread, confirmed by Phil as likely fabricated

Test plan

• Verify the updated line reads naturally in context on the published page

🤖 Generated with Claude Code

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[claude]

Claude finished @samgutentag's task in 35s —— View job

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PR Review

• Read changed file and diff
• Review for typos, grammar, formatting, and documentation best practices

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Change reviewed: merge-queue/optimizations/anti-flake-protection.md line 27

Before:

Flaky tests cause 20-40% of PR failures in typical pipelines.

After:

Flaky tests frequently cause PR failures unrelated to actual code changes.

The replacement is clean, reads naturally, and is accurate without requiring a source. The added phrase "unrelated to actual code changes" is a nice improvement — it reinforces why this matters to developers.

Minor observation (pre-existing, not introduced by this PR): The bullet is labeled "Eliminate false negatives" but flaky tests blocking valid PRs are technically false positives (a test fails when the code is fine). This is not a blocker for this PR, but worth a future cleanup for accuracy.

No blocking issues. This is a good, focused fix.

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[github-actions]

Auto-approved: Claude code review passed.