docs(compute/metadata): update OnGCE description (#10408)

We are using the `metadata.OnGCE()` function to check if it runs on our Cloud Runs, this can be a helpful comment for others using the package.

compute/metadata/metadata.go

@@ -110,7 +110,7 @@ var (
 	onGCE     bool
 )
 
-// OnGCE reports whether this process is running on Google Compute Engine.
+// OnGCE reports whether this process is running on Google Compute Platforms.
 func OnGCE() bool {
 	onGCEOnce.Do(initOnGCE)
 	return onGCE