issue/pr create: exit with nonzero status code when "Cancel" was chosen

This is to indicate that the command had not finished successfully.

pkg/cmd/issue/create/create.go

@@ -249,6 +249,7 @@ func createRun(opts *CreateOptions) (err error) {
 
 		if action == prShared.CancelAction {
 			fmt.Fprintln(opts.IO.ErrOut, "Discarding.")
+			err = cmdutil.SilentError
 			return
 		}
 	} else {

pkg/cmd/pr/create/create.go

@@ -299,7 +299,8 @@ func createRun(opts *CreateOptions) (err error) {
 
 	if action == shared.CancelAction {
 		fmt.Fprintln(opts.IO.ErrOut, "Discarding.")
-		return nil
+		err = cmdutil.SilentError
+		return
 	}
 
 	err = handlePush(*opts, *ctx)