Prepare release 6.4.0

Author: XWB

CHANGELOG-6.0.md

@@ -4,7 +4,7 @@ CHANGELOG for 6.x
 This changelog references the relevant changes (bug and security fixes) done
 in 6.x versions.
 
-### 6.4.0 (2024-xx-xx)
+### 6.4.0 (2024-05-13)
 * Added PHP 8.3 support.
 * Added Symfony 7.0 support.
 * Added Symfony 6.4 support.