Merge branch '5.1' into 5.2

* 5.1:
  Dont allow unserializing classes with a destructor
  Dont allow unserializing classes with a destructor - 4.4
  [Cache] fix possible collision when writing tmp file in filesystem adapter
  a colon followed by spaces exclusively separates mapping keys and values
  Contracts: Remove ellipsis
  fix handling float-like key attribute values
  Fix missing BCC recipients in SES bridge
  Dont allow unserializing classes with a destructor - 5.1

Author: nicolas-grekas

Transport/Smtp/SmtpTransport.php

@@ -340,6 +340,16 @@ private function checkRestartThreshold(): void
         $this->restartCounter = 0;
     }
 
+    public function __sleep()
+    {
+        throw new \BadMethodCallException('Cannot serialize '.__CLASS__);
+    }
+
+    public function __wakeup()
+    {
+        throw new \BadMethodCallException('Cannot unserialize '.__CLASS__);
+    }
+
     public function __destruct()
     {
         $this->stop();