runtime: skip TestG0StackOverflow on ios

runtime: skip TestG0StackOverflow on ios

This test fails when run on ios. (Although ios does not normally
support "exec", in the corellium environment it does.)

For #26061.

Change-Id: Idfdc53758aaabf0cb87ae50f9a4666deebf57fd6
Reviewed-on: https://go-review.googlesource.com/c/go/+/487355
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>