Merge forwardport of #13044 to 2.3-develop branch

Applied pull request patch https://github.com/magento/magento2/pull/13044.patch (created by @torhoehn) based on commit(s):
  1. 9ab75ba
  2. 93453a8

Fixed GitHub Issues in 2.3-develop branch:
  - #12876: Multiple newsletter confirmation emails sent (reported by @nfourteen)

Author: magento-engcom-team

app/code/Magento/Newsletter/Model/Subscriber.php

@@ -604,14 +604,20 @@ protected function _updateCustomerSubscription($customerId, $subscribe)
 
         $this->save();
         $sendSubscription = $sendInformationEmail;
-        if ($sendSubscription === null xor $sendSubscription) {
+        if ($sendSubscription === null xor $sendSubscription && $this->isStatusChanged()) {
             try {
-                if ($isConfirmNeed) {
-                    $this->sendConfirmationRequestEmail();
-                } elseif ($this->isStatusChanged() && $status == self::STATUS_UNSUBSCRIBED) {
-                    $this->sendUnsubscriptionEmail();
-                } elseif ($this->isStatusChanged() && $status == self::STATUS_SUBSCRIBED) {
-                    $this->sendConfirmationSuccessEmail();
+                switch ($status) {
+                    case self::STATUS_UNSUBSCRIBED:
+                        $this->sendUnsubscriptionEmail();
+                        break;
+                    case self::STATUS_SUBSCRIBED:
+                        $this->sendConfirmationSuccessEmail();
+                        break;
+                    case self::STATUS_NOT_ACTIVE:
+                        if ($isConfirmNeed) {
+                            $this->sendConfirmationRequestEmail();
+                        }
+                        break;
                 }
             } catch (MailException $e) {
                 // If we are not able to send a new account email, this should be ignored