Add non regression test

Author: VincentLanglet

tests/PHPStan/Rules/Classes/EnumSanityRuleTest.php

@@ -179,4 +179,15 @@ public function testBug13768(): void
 		]);
 	}
 
+	#[RequiresPhp('>= 8.1')]
+	public function testBug11891(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-11891.php'], [
+			[
+				'Enum test has duplicate value 42 for cases A, B.',
+				3,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Classes/data/bug-11891.php

@@ -0,0 +1,8 @@
+<?php // lint >= 8.1
+
+namespace Bug11891;
+
+enum test:int {
+	case A = 42;
+	case B = self::A->value;
+};