* ping/go: tidy with compat flag to prevent errors in CI
```
unused github.com/whyrusleeping/multiaddr-filter
unused golang.org/x/xerrors
go: downloading github.com/google/go-cmp v0.5.6
github.com/libp2p/test-plans/ping/go imports
github.com/testground/sdk-go/sync imports
nhooyr.io/websocket tested by
nhooyr.io/websocket.test imports
nhooyr.io/websocket/internal/test/assert imports
github.com/google/go-cmp/cmp loaded from github.com/google/go-cmp@v0.5.5,
but go 1.16 would select v0.5.6
...
```
* ping/go: update to go1.18