L2SS-869: fix unit test

tangostationcontrol/tangostationcontrol/statistics/writer/hdf5.py

@@ -374,6 +374,9 @@ class BstHdf5Writer(HDF5Writer):
     def new_collector(self):
         return BSTCollector()
     
+    def retrieve_attribute_values(self):
+        pass
+
     def write_values_matrix(self, current_group):
         # store the BST values
         current_group.create_dataset(
@@ -414,6 +417,9 @@ class XstHdf5Writer(HDF5Writer):
             f"{time_str}{suffix}"
         )
     
+    def retrieve_attribute_values(self):
+        pass
+
     def write_values_matrix(self, current_group):
         # requires a function call to transform the xst_blocks in to the right
         # structure