runtime: soften up the GCTestIsReachable test a bit
This test can fail due to objects being incorrectly retained due
to conservative scanning. Allow a bit of slop (1 accidentally
retained object) to prevent flaky failures.
Fixes #67204
"fixes" is a bit too strong a word. More like, hopefully reduces
the false positive rate to something approaching 0.
Change-Id: I09984f0cce50d8209aef19f3d89b0e295c86f8d1
Reviewed-on: https://go-review.googlesource.com/c/go/+/590615 Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>