docs(core): Document TestBed.get deprecation (#32974)

It was replaced by TestBed.inject, documenting such change.

PR Close #32974

aio/content/guide/deprecations.md

@@ -29,6 +29,7 @@ v5 - v8
 v6 - v9
 v7 - v10
 v8 - v11
+v9 - v12
 -->
 
 
@@ -51,6 +52,7 @@ v8 - v11
 | `@angular/core` | [`defineInjectable`](#core) | v11 |
 | `@angular/router` | [`loadChildren` string syntax](#loadChildren) | v11 |
 | `@angular/router` | [`ActivatedRoute` params and `queryParams` properties](#activatedroute-props) | unspecified |
+| `@angular/core/testing` | [`TestBed.get`](#testing) | v12 |
 
 
 
@@ -86,6 +88,14 @@ Tip: In the [API reference section](api) of this doc site, deprecated APIs are i
 | [`ANALYZE_FOR_ENTRY_COMPONENTS`](api/core/ANALYZE_FOR_ENTRY_COMPONENTS) | none | v9 | See [`ANALYZE_FOR_ENTRY_COMPONENTS`](#entryComponents) |
 
 
+{@a testing}
+### @angular/core/testing
+
+| API | Replacement | Deprecation announced | Notes |
+| --- | ----------- | --------------------- | ----- |
+| [`TestBed.get`](api/core/testing/TestBed#get) | [`TestBed.inject`](api/core/testing/TestBed#inject) | v9 | Same behavior, but type safe. |
+
+
 {@a forms}
 ### @angular/forms
 

aio/content/guide/testing.md

@@ -357,11 +357,15 @@ array of the services that you'll test or mock.
 
 Then inject it inside a test by calling `TestBed.inject()` with the service class as the argument.
 
+<div class="alert is-helpful">
+
 **Note:** We used to have `TestBed.get()` instead of `TestBed.inject()`.
 The `get` method wasn't type safe, it always returned `any`, and this is error prone.
 We decided to migrate to a new function instead of updating the existing one given
 the large scale use that would have an immense amount of breaking changes.
 
+</div>
+
 <code-example
   path="testing/src/app/demo/demo.testbed.spec.ts"
   region="value-service-inject-it">
@@ -1065,7 +1069,7 @@ The component injector is a property of the fixture's `DebugElement`.
   header="WelcomeComponent's injector">
 </code-example>
 
-{@a testbed-get}
+{@a testbed-inject}
 
 #### _TestBed.inject()_
 
@@ -3079,8 +3083,8 @@ Here are the most important static methods, in order of likely utility.
 
   <tr>
     <td style="vertical-align: top">
-      {@a testbed-get}
+      {@a testbed-inject}
-      <code>get</code>
+      <code>inject</code>
     </td>
 
     <td>