Fix hass_storage not clearing task (#95209)

hass_storage would never allow another load if the
no data path was hit

discovered while writing tests for https://github.com/home-assistant/core/pull/95202

tests/common.py

@@ -1218,6 +1218,8 @@ def mock_storage(
         if store._data is None:
             # No data to load
             if store.key not in data:
+                # Make sure the next attempt will still load
+                store._load_task = None
                 return None
 
             mock_data = data.get(store.key)