Merge branch '6.0' into 6.1

* 6.0:
  [Serializer] Fix denormalizing union types
  [HttpFoundation] Remove obsolete override
  bug #42637 [Security] Fixed TOCTOU in RememberMe cache token verifier
  Fix compatibility of ldap 6.0 with security 5.x
  Add missing upgrade note for ldap
  [Mailer] Preserve case of headers

Author: nicolas-grekas

CHANGELOG.md

@@ -4,7 +4,7 @@ CHANGELOG
 6.1
 ---
 
-* Make `start()` and `stop()` methods public on `SmtpTransport`
+ * Make `start()` and `stop()` methods public on `SmtpTransport`
 
 6.0
 ---