L2SS-869: fix unit test

tangostationcontrol/tangostationcontrol/statistics/writer/hdf5.py

@@ -373,6 +373,9 @@ 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
@@ -413,6 +416,9 @@ class XstHdf5Writer(HDF5Writer):
             f"{self.file_location}/{self.mode}_SB{self.subband_index}_"
             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