Added regression test

Author: staabm

tests/PHPStan/Analyser/nsrt/bug-12173.php

@@ -0,0 +1,19 @@
+<?php // lint >= 7.4
+
+namespace Bug12173;
+
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+	public function parse(string $string): void
+	{
+		$regex = '#.*(?<fruit>(apple|orange)).*#';
+
+		if (preg_match($regex, $string, $matches) !== 1) {
+			throw new \Exception('Invalid input');
+		}
+
+		assertType("'apple'|'orange'", $matches['fruit']);;
+	}
+}