Merge branch '5.1' into 5.2

* 5.1:
  Use more explicit variable name
  Fix wrong comment about SES region
  [Mailer] [Sendgrid] Use $scheme variable to stay consistent
  [Mailer] [Amazon] Fix @param annotation
  [Mailer] Rename testsuites
  Remove void return type from test methods
  Remove void return type from test methods
  [Notifier] Remove void return type from test methods

Author: derrabus

Tests/ContainerAwareEventManagerTest.php

@@ -156,7 +156,7 @@ class MyListener
     public $calledByInvokeCount = 0;
     public $calledByEventNameCount = 0;
 
-    public function __invoke(): void
+    public function __invoke()
     {
         ++$this->calledByInvokeCount;
     }