Fix for registering scheduled tasks (#6815) (#6816)

- Closes https://github.com/inventree/InvenTree/issues/6793

(cherry picked from commit 9576b50152)

Co-authored-by: Oliver <oliver.henry.walters@gmail.com>

InvenTree/plugin/base/integration/ScheduleMixin.py

@@ -112,7 +112,7 @@ class ScheduleMixin:
     @property
     def has_scheduled_tasks(self):
         """Are tasks defined for this plugin."""
-        return bool(self.scheduled_tasks)
+        return bool(self.get_scheduled_tasks())
 
     def validate_scheduled_tasks(self):
         """Check that the provided scheduled tasks are valid."""

InvenTree/plugin/plugin.py

@@ -138,7 +138,13 @@ class MixinBase:
             if fnc_name is True:
                 return True
 
-            return getattr(self, fnc_name, True)
+            attr = getattr(self, fnc_name, True)
+
+            if callable(attr):
+                return attr()
+            else:
+                return attr
+
         return False
 
     def add_mixin(self, key: str, fnc_enabled=True, cls=None):