refactor(forms): use strict equality for pending status getter

The `pending` getter in `AbstractControl` used loose equality (`==`)
while all other status getters (`valid`, `invalid`, `disabled`) use
strict equality (`===`). Both sides are strings so behavior is
identical, but this inconsistency would fail strict linting rules.

packages/forms/src/model/abstract_model.ts

@@ -658,7 +658,7 @@ export abstract class AbstractControl<
    * false otherwise.
    */
   get pending(): boolean {
-    return this.status == PENDING;
+    return this.status === PENDING;
   }
 
   /**