testing: enforce -skip in example tests
The go test flag -skip had no effect in example tests.
Fixes #61482
Change-Id: I28dfddb88fef3fead2a3c74f9cb63a674a768231
GitHub-Last-Rev:
e8c3c3460af906f4c7be7f7a8b4a4c60b71fcec1
GitHub-Pull-Request: golang/go#61491
Reviewed-on: https://go-review.googlesource.com/c/go/+/511837
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>