runtime: skip TestNoShrinkStackWhileParking on openbsd
runtime: skip TestNoShrinkStackWhileParking on openbsd

The test has proven to be flaky on OpenBSD since March, and there
hasn't been progress on resolving this finding. Mark the test as
flaky to so that this problem doesn't block the Go 1.19 release.

Updates #51482.

Change-Id: I92ad7498c20cfa94565880363bec85f9a4f3e916
Reviewed-on: https://go-review.googlesource.com/c/go/+/401335
Run-TryBot: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Auto-Submit: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Reviewed-by: Michael Pratt <e7f1edc6d5aa9f6c8c377425db8f1a5816cbbb88@google.com>

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