fix: import deprecate from documented module

The internal `deprecate` wrapper imports Ember's deprecation utility
from a different location than the documented one.

When running this addon against the latest version of Ember, a runtime
error occurs where Ember's deprecation function is not defined.

`deprecate` documentation: https://api.emberjs.com/ember/3.24/functions/@ember%2Fdebug/deprecate

addon-test-support/-private/deprecate.js

@@ -1,4 +1,4 @@
-import { deprecate as emberDeprecate } from '@ember/application/deprecations';
+import { deprecate as emberDeprecate } from '@ember/debug';
 
 const NAMESPACE = 'ember-cli-page-object';