[GP-CLI] fix gp preview not outputting stderr and stdout properly (#20166)

* [GP-CLI] fix `gp preview` not outputting stderr and stdout properly

* remove stdout pipe

Author: mustard-mh

components/gitpod-cli/cmd/preview.go

@@ -84,6 +84,7 @@ func openPreview(gpBrowserEnvVar string, url string) error {
 	args = append(args, url)
 
 	previewCmd := exec.Command(pcmd, args...)
+	previewCmd.Stderr = os.Stderr
 	err = previewCmd.Run()
 	if err != nil {
 		return err