[CodeQuality] Simplify single-statement void callback in CallbackSingleAssertToSimplerRector

[TomasVotruba]

Extends CallbackSingleAssertToSimplerRector to also simplify callbacks that hold a single assertSame() statement with no return true; (a void callback), not only the two-statement assertSame() + return true; shape.

 $this->mockModel->expects($this->once())
     ->method('queueWebhooksByType')
-    ->with($this->callback(function ($type): void {
-        $this->assertSame($type, 'some_value');
-    }));
+    ->with($this->equalTo('some_value'));

Multi-statement callbacks are still skipped.