Update bug-13857.php

Author: staabm

tests/PHPStan/Analyser/nsrt/bug-13857.php

@@ -41,3 +41,11 @@ function testUnionArray(array $array, int $id): void {
 	// only one element was set to 'foo', not all of them.
 	assertType("non-empty-array<int, non-empty-array{foo?: int, state?: string}>", $array);
 }
+
+/**
+ * @param array<int, array{state: string}|array{foo: int}> $array
+ */
+function testUnionArrayDifferentType(array $array, int $id): void {
+	$array[$id]['state'] = true;
+	assertType("non-empty-array<int, array{state: string}|non-empty-array{foo?: int, state?: true}>", $array);
+}