Add the missing versionadded directive

Author: javiereguiluz

reference/constraints/PasswordStrength.rst

@@ -1,6 +1,10 @@
 PasswordStrength
 ================
 
+.. versionadded:: 6.3
+
+    The ``PasswordStrength`` constraint was introduced in Symfony 6.3.
+
 Validates that the given password has reached the minimum strength required by
 the constraint.
 
@@ -15,7 +19,7 @@ Basic Usage
 
 The following constraint ensures that the ``rawPassword`` property of the
 ``User`` class reaches the minimum strength required by the constraint.
-By default, the minimum required score is 2.
+By default, the minimum required score is ``2``.
 
 .. configuration-block::