Update target PHP version to 8

.phan/config.php

@@ -3,7 +3,7 @@
 declare(strict_types=1);
 
 return [
-	'target_php_version' => '7.2',
+	'target_php_version' => '8.0',
 
 	'directory_list' => [
 		'.phan/stubs/',
@@ -40,7 +40,7 @@ return [
 		// Infer values from phpunit tests
 		//'PHPUnitAssertionPlugin'
 		// Warn if structures are missing phpdoc plugins
-		//'HasPHPDocPlugin'
+		'HasPHPDocPlugin',
 		// warn on isset(func()['index']) and isset($array[$key]) where $array is not set
 		//'InvalidVariableIssetPlugin'
 		// warn about returning non-array values from __sleep