Allow reinitialization of a readonly property in __clone since PHP8.3

[takaram]

Closes phpstan/phpstan#11495

[ondrejmirtes]

I'd like to have more tests here:

1. To verify double assignment is still detected as error (https://3v4l.org/oaLm9)
2. To verify assignment to something else than $this is detected as error:

	public function __clone()
	{
		$s = new self();
		$s->foo = 'baz';
	}

[takaram]

I added a test for 2.

For 1., no error is reported on double assignment. This looks not so easy to implement.
I'll take a deeper look...