Replace assertInternalType('boolean', ...) with assertIsBool(...) bec…

…ause it's been deprecated

tests/EnumAccessorTest.php

@@ -116,7 +116,7 @@ public function it_can_still_read_casted_fields()
 
         $this->assertNotNull($order->id);
         $this->assertInstanceOf(\DateTime::class, $order->created_at);
-        $this->assertInternalType('boolean', $order->is_active);
+        $this->assertIsBool($order->is_active);
     }
 
     /**