[Module] Add return type hint to isPublicModule (#7758)

Add a return type hint to the isPublicModule method.

Resolves #4282

Author: driusan

modules/api/php/module.class.inc

@@ -35,7 +35,7 @@ class Module extends \Module
      *
      * @return bool
      */
-    public function isPublicModule()
+    public function isPublicModule() : bool
     {
         // The API is "public"  because the login endpoint needs to be public.
         return true;

modules/login/php/module.class.inc

@@ -19,7 +19,7 @@ class Module extends \Module
      *
      * @return bool true
      */
-    public function isPublicModule()
+    public function isPublicModule() : bool
     {
         return true;
     }

php/libraries/Module.class.inc

@@ -225,7 +225,7 @@ abstract class Module extends \LORIS\Router\PrefixRouter
      * @return bool False. Subclasses must override this function in the case
      *                  that they should be publicly available.
      */
-    public function isPublicModule()
+    public function isPublicModule() : bool
     {
         return false;
     }