sync:cpu10: TestPoolGC failures

[gopherbot]

#!watchflakes
default <- pkg ~ `sync:cpu10` && test == "TestPoolGC"

Issue created automatically to collect these failures.

Example (log):

=== RUN   TestPoolGC
    pool_test.go:131: only 60 out of 100 resources are cleaned up on try 0
--- FAIL: TestPoolGC (1.08s)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "sync:cpu10" && test == "TestPoolGC"

2025-05-09 00:40 gotip-linux-amd64-newinliner go@0c8615be sync:cpu10.TestPoolGC (log)

=== RUN   TestPoolGC
    pool_test.go:131: only 60 out of 100 resources are cleaned up on try 0
--- FAIL: TestPoolGC (1.08s)

— watchflakes

[gopherbot]

Change https://go.dev/cl/671675 mentions this issue: sync: use blockUntilCleanupQueueEmpty instead of busy-looping in tests

[gopherbot]

Change https://go.dev/cl/671676 mentions this issue: runtime: prevent cleanup goroutines from missing work