PDOStatement::$queryString "readonly" is not properly implemented

Description

The following code:

<?php
$stmt = new PDOStatement();
var_dump($stmt);
for($i=0;$i<10;$i++)
        $stmt->queryString = (string) $i;
var_dump($stmt);

Resulted in this output:

object(PDOStatement)#1 (0) {
  ["queryString"]=>
  uninitialized(string)
}
object(PDOStatement)#1 (1) {
  ["queryString"]=>
  string(1) "9"
}

But I expected this output instead:

object(PDOStatement)#1 (0) {
  ["queryString"]=>
  uninitialized(string)
}
Fatal error: Uncaught Error: Property queryString is read only in x.php:5

The reason this happens is because the following code is wrong:
https://github.com/php/php-src/blob/209e0d6ad29b1f49982c58088aadd9d1ad86a162/ext/pdo/pdo_stmt.c#L2008-L2014
The second loop iteration just reuses the cache slot and won't go through the write handler, bypassing the fake readonly check.
Either this should be relaxed or be fixed (i.e. "real readonly").

PHP Version

8.3+

Operating System

No response

Start by reading ext/pdo/pdo_stmt.c at the linked lines and run the reproduction from the issue. Done means repeated assignments to PDOStatement::$queryString no longer bypass the readonly check and produce the expected Error; an open pull request already addresses this issue.