cmd: update golang.org/x/telemetry to 38c23d2

cmd: update golang.org/x/telemetry to 38c23d2

Commands run:
    go get golang.org/x/telemetry@38c23d2
    go mod tidy
    go mod vendor

This also pulls in golang.org/x/sync@v0.8.0 as a module requirement, but
no changes need to be vendored from that module.

Change-Id: I2238388b6dc2a4a29a53e7b8ddea29eb677a97b7
Reviewed-on: https://go-review.googlesource.com/c/go/+/603898
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>