fix(@angular/cli): show error when using non-TTY terminal without passing --skip-confirmation during ng add

Closes #21512

(cherry picked from commit c0f1b5e)

Author: alan-agius4

packages/angular/cli/commands/add-impl.ts

@@ -185,7 +185,7 @@ export class AddCommand extends SchematicCommand<AddCommandSchema> {
       );
 
       if (!confirmationResponse) {
-        if (!isTTY) {
+        if (!isTTY()) {
           this.logger.error(
             'No terminal detected. ' +
               `'--skip-confirmation' can be used to bypass installation confirmation. ` +