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

DebugClassLoader.php

@@ -67,10 +67,11 @@ class DebugClassLoader
         'string' => 'string',
         'self' => 'self',
         'parent' => 'parent',
+        'mixed' => 'mixed',
     ] + (\PHP_VERSION_ID >= 80000 ? [
+        'static' => 'static',
         '$this' => 'static',
     ] : [
-        'mixed' => 'mixed',
         'static' => 'object',
         '$this' => 'object',
     ]);