CI: flaky test pooledMap() under async/pool_test.ts failing on canary, macOS-latest

[lionel-rowe]

Describe the bug

Steps to Reproduce

See https://github.com/denoland/std/actions/runs/12434613872/job/34718689863?pr=6286

Message isn't very helpful but it's from line 22:

assert(diff < 300);

As well as fixing the flaky test, that should probably be switched out for assertLess for better error output.

Expected behavior

Test passes

Environment

CI canary, macOS-latest env