test: add @var for PHPStan

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  Line   tests/system/Models/FindModelTest.php
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  50     Cannot access property $name on array<int, array>.
  51     Cannot access property $email on array<int, array>.
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Author: kenjis

tests/system/Models/FindModelTest.php

@@ -45,6 +45,7 @@ public function testFindReturnsEntityWithCasts(): void
         ]);
         $id = $this->model->insert($user, true);
 
+        /** @var UserWithCasts $user */
         $user = $this->model->find($id);
 
         $this->assertSame('John Smith', $user->name);