test: don't run fixedbugs/issue11656.go on netbsd/386

The netbsd/386 builder reports a failure at
http://build.golang.org/log/c21c45a4fc6f4845868aa3ebde0f5bb3f167f3a3

I'm assuming that this is similar to the unknown openbsd failure.

Update #11910.

Change-Id: I9cdfefa23dc7cda3849f14814b3ce531f1d39e93
Reviewed-on: https://go-review.googlesource.com/12777


Reviewed-by: David Crawshaw <crawshaw@golang.org>