Upgrade to Angular 21 and update related dependencies in package.json and package-lock.json

Migration Changes
 [router-current-navigation] Replaces usages of the deprecated  Router.getCurrentNavigation method with the Router.currentNavigation signal.

All structural directives in the application's templates have been replaced with the new, built-in block control flow syntax.

Author: marthamwangi

README.md

@@ -3,7 +3,7 @@
 
 This repository contains the code of the [Angular Testing Course](https://angular-university.io/course/angular-testing-course).
 
-This course repository is updated to Angular v20, and there is a  package-lock.json file available, for avoiding semantic versioning installation issues.
+This course repository is updated to Angular v21, and there is a  package-lock.json file available, for avoiding semantic versioning installation issues.
 
 ![Angular Testing Course](https://s3-us-west-1.amazonaws.com/angular-university/course-images/angular-testing-small.png)