This allows to skip the last part of the test under GopherJS as well as
WebAssembly, since GopherJS shares GOOS=js with wasm.

Change-Id: I41adad788043c1863b23eb2a6da9bc9aa2833092
GitHub-Last-Rev: d8d42a3b7ccb2bee6479306b6ac1a319443702ec
GitHub-Pull-Request: golang/go#51827
Reviewed-on: https://go-review.googlesource.com/c/go/+/394114


Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Sean Liao <sean@liao.dev>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: Sean Liao <sean@liao.dev>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>