Prepare the 2.15.1 release

CHANGELOG

@@ -1,4 +1,4 @@
-# 2.15.1 (2022-XX-XX)
+# 2.15.1 (2022-05-17)
 
 * Fix optimizing non-public named closures
 

src/Environment.php

@@ -38,12 +38,12 @@ use Twig\TokenParser\TokenParserInterface;
  */
 class Environment
 {
-    public const VERSION = '2.15.1-DEV';
+    public const VERSION = '2.15.1';
     public const VERSION_ID = 21501;
     public const MAJOR_VERSION = 2;
     public const MINOR_VERSION = 15;
     public const RELEASE_VERSION = 1;
-    public const EXTRA_VERSION = 'DEV';
+    public const EXTRA_VERSION = '';
 
     private $charset;
     private $loader;