Added regression test for #11968

- New integration test testBug11968 in AnalyserIntegrationTest
- Test data file with 500-case UnitEnum with match expression and method calls
- Covers the pattern from the issue: large enum with match($this) returning strings
- Ensures analysis of large enums completes in reasonable time without errors

Closes phpstan/phpstan#11968

Author: staabm

tests/PHPStan/Analyser/AnalyserIntegrationTest.php

@@ -1462,6 +1462,13 @@ public function testBug11263(): void
 		$this->assertNoErrors($errors);
 	}
 
+	#[RequiresPhp('>= 8.1')]
+	public function testBug11968(): void
+	{
+		$errors = $this->runAnalyse(__DIR__ . '/data/bug-11968.php');
+		$this->assertNoErrors($errors);
+	}
+
 	#[RequiresPhp('>= 8.0')]
 	public function testBug11147(): void
 	{