build: Skip Phan on PHP 8.1

GitHub CI, this library still supports PHP 8.1, validated from time
to time there. Phan only needs to run once, the version doesn't
matter.

Change-Id: If1ec3f2618eb1bbef0a6967afa6b49caa4b19ea2

Author: Krinkle

.phan/config.php

@@ -1,5 +1,10 @@
 <?php
 
+if ( PHP_VERSION_ID < 80200 ) {
+	print "Skipping Phan on PHP 8.1.\n\n";
+	exit( 0 );
+}
+
 return [
 
 	'target_php_version' => '8.1',