os/signal: increase deliver time for signal testcase

This increases the time to wait for signals to be delivered in the
TestAtomicStop testcase. When running gccgo tests on ppc64 or ppc64le,
there are intermittent failures in this test because the wait time is
too small.

Updates golang/go#29046

Change-Id: Ic70f4109f328df95d50270f468a4860fa3c1e286
Reviewed-on: https://go-review.googlesource.com/c/153879
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed