Fix cache-hit in flakiness detection performance test (#8482) We don't want build cache hit in performance flakiness detection, however, previously the coordinator build resolves "flakiness-detection-commit" baseline to real commit id "5.3-commit-237a600", resulting in unexpected cache hit.
This PR fixes it by:
- On coordinator's side, pass "flakiness-detection-commit" as it is to worker build. - On worker's side, worker build resolves "flakiness-detection-commit" to real commit version - this disables build cache.
Since `DetermineBaselines` is becoming more and more complex, this PR also adds a unit test for `DetermineBaselines` class.