Add non-regression test for phpstan/phpstan#1311

Verifies that by-reference foreach without key variable correctly tracks
type overwrites when casting values (e.g. `$item = (string) $item`).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

tests/PHPStan/Analyser/nsrt/bug-1311.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Bug1311;
+
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+	/**
+	 * @var array<int, string>
+	 */
+	private $list = [];
+
+	/**
+	 * @param array<int, int> $temp
+	 */
+	public function convertList(array $temp): void
+	{
+		foreach ($temp as &$item) {
+			$item = (string) $item;
+		}
+
+		assertType('array<int, lowercase-string&numeric-string&uppercase-string>', $temp);
+
+		$this->list = $temp;
+	}
+}