Merge branch '5.1' into 5.2

* 5.1:
  µCS fix
  CS fix
  CS fix
  [travis] use PHP 8.0 to patch return types and run deps=low
  Add me as a Notifier code owner
  Update sl_SI translations
  Don't trigger deprecation for deprecated aliases pointing to deprecated definitions
  [HttpFoundation] use atomic writes in MockFileSessionStorage
  Make EmailMessage & SmsMessage transport nullable
  remove unused argument
  [DI] fix param annotation
  [Config] Add \Symfony\Component\Config\Loader::load() return type
  Simplify PHP CS Fixer config
  Rename normalize param

Author: nicolas-grekas

Message/EmailMessage.php

@@ -102,11 +102,14 @@ public function getOptions(): ?MessageOptionsInterface
     /**
      * @return $this
      */
-    public function transport(string $transport): self
+    public function transport(?string $transport): self
     {
         if (!$this->message instanceof Email) {
             throw new LogicException('Cannot set a Transport on a RawMessage instance.');
         }
+        if (null === $transport) {
+            return $this;
+        }
 
         $this->message->getHeaders()->addTextHeader('X-Transport', $transport);
 

Message/SmsMessage.php

@@ -83,7 +83,7 @@ public function getSubject(): string
     /**
      * @return $this
      */
-    public function transport(string $transport): self
+    public function transport(?string $transport): self
     {
         $this->transport = $transport;