Fix checkGenericClassInNonGenericObjectType PHPStan errors

This commit removes the checkGenericClassInNonGenericObjectType flag
from PHPStan configuration files and fixes all associated errors in our
code base.

[MAILPOET-3236]

lib/Entities/NewsletterLinkEntity.php

@@ -50,7 +50,7 @@ class NewsletterLinkEntity {
    * If we didn't specify extra lazy the function would load all clicks and count them. This way it uses a single count query.
    * @ORM\OneToMany(targetEntity="MailPoet\Entities\StatisticsClickEntity", mappedBy="link", fetch="EXTRA_LAZY")
    *
-   * @var StatisticsClickEntity[]|ArrayCollection
+   * @var ArrayCollection<int, StatisticsClickEntity>
    */
   private $clicks;