Add test for nested array reference tracking limitation

Nested arrays like `[[&$a]]` don't propagate reference updates through
`$b[0][0] = 2` to `$a`. This documents the current behavior as a known
limitation of the array reference tracking implementation.

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

Author: phpstan-bot

tests/PHPStan/Analyser/nsrt/bug-14333.php

@@ -32,3 +32,23 @@ function testMultipleByRefInArray(): void
 	assertType('2', $a);
 	assertType("'bar'", $c);
 }
+
+function testNested(): void
+{
+	$a = 1;
+
+	$b = [[&$a]];
+	assertType('1', $a);
+
+	$b[0][0] = 2;
+
+	assertType('1', $a); // Should be 2 in real PHP, but nested array reference tracking is not implemented
+
+	$b[0] = [];
+
+	assertType('1', $a);
+
+	$b[0][0] = 3;
+
+	assertType('1', $a);
+}