runtime: skip TestPingPongHog in race mode

runtime: skip TestPingPongHog in race mode

TestPingPongHog tests properties of the scheduler.
But the race detector intentionally does randomized scheduling,
so the test is not applicable.

Fixes #38266

Change-Id: Ib06aa317b2776cb1faa641c4e038e2599cf70b2d
Reviewed-on: https://go-review.googlesource.com/c/go/+/227344
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>