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

UnicodeString.php

@@ -359,6 +359,10 @@ public function startsWith($prefix): bool
 
     public function __wakeup()
     {
+        if (!\is_string($this->string)) {
+            throw new \BadMethodCallException('Cannot unserialize '.__CLASS__);
+        }
+
         normalizer_is_normalized($this->string) ?: $this->string = normalizer_normalize($this->string);
     }