runtime: convert local var stop at TestAfterStress to atomic type
runtime: convert local var stop at TestAfterStress to atomic type

For #53821

Change-Id: I7e86dac34691f7752f68879ff379061f3435cd45
Reviewed-on: https://go-review.googlesource.com/c/go/+/427139
Reviewed-by: Michael Knyszek <4473450dc5c88f06e1fb787f303d7805ec2aee65@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Run-TryBot: xie cui <445dd9517fbe3a6bac75d0d2795bff146b58b184@qq.com>
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go