[infra] Unexpected results/flakiness showed when running rolldown heavily in the same time

First attempt

<img width="1214" height="1206" alt="Image" src="https://github.com/user-attachments/assets/afef52ba-12ce-4226-98fb-728eb1cbea53" />

https://github.com/rolldown/rolldown/blob/92523226d53337356753cc043fc5e3609d6c6a3e/packages/rolldown/tests/fixture.test.ts#L18