add NSRT test

Author: schlndh

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

@@ -0,0 +1,24 @@
+<?php declare(strict_types = 1);
+
+namespace OptionalArrayKeyInMultiDimArrayLoop;
+
+/**
+ * @param array<int, array{1: int, 2: int, 3: float}> $rows
+ */
+function foo(array $rows): mixed
+{
+	$itemMap = [];
+
+	foreach ($rows as $row) {
+		$x = $row[1];
+		$month = $row[2];
+
+		$itemMap[$x][$month]['foo'] ??= 5;
+		$itemMap[$x][$month]['bar'] ??= 5;
+
+		\PHPStan\Testing\assertType('array{foo: 5, bar: 5, amount?: 0.0}', $itemMap[$x][$month]);
+		$itemMap[$x][$month]['amount'] ??= 0.0;
+	}
+
+	return $itemMap;
+}