Fix MailPoet\WP\Functions newly added method name

[MAILPOET-4703]

mailpoet/lib/Router/Endpoints/Subscription.php

@@ -108,7 +108,7 @@ class Subscription {
   }
 
   private function applyOneClickUnsubscribeStrategy($data): void {
-    if (!$this->wp->isSiteUsingHttps()) {
+    if (!$this->wp->wpIsSiteUrlUsingHttps()) {
       return;
     }
     $subscription = $this->initSubscriptionPage(UserSubscription\Pages::ACTION_UNSUBSCRIBE, $data);

mailpoet/lib/WP/Functions.php

@@ -848,7 +848,7 @@ class Functions {
     return is_wp_error($value);
   }
 
-  public function isSiteUsingHttps(): bool {
+  public function wpIsSiteUrlUsingHttps(): bool {
     return wp_is_site_url_using_https();
   }
 }