WP107 #788: Added boolean as return option for getApiKey method

Ref it/site/w4.uib.no#788

src/ApiConnectorInterface.php

@@ -14,10 +14,10 @@ interface ApiConnectorInterface {
   /**
    * Returns the api key.
    *
-   * @return string|bool
+   * @return string|false
    *   The api key.
    */
-  public function getApiKey(): string|bool;
+  public function getApiKey(): string|false;
 
   /**
    * Returns the base url of the api_connector.