[CodeQuality] Skip anonymous classes in AssertClassToThisAssertRector

[TomasVotruba]

An anonymous class defined inside a test method has its own $this scope, which is not the TestCase. Rewriting Assert::assertSame() to $this->assertSame() there produces a call to a method that does not exist.

 final class SomeTest extends TestCase
 {
     public function testMe()
     {
         $repository = new class() {
             public function getEntities(array $args = []): array
             {
-                Assert::assertSame(['key' => 'value'], $args);
+                Assert::assertSame(['key' => 'value'], $args); // kept as is

                 return [];
             }
         };
     }
 }

The rule now stops traversing when it enters a Class_ node, same way it already stops on static closures.