fix: indexing error in median calculation

Author: janezicmatej

observer/voting_round.py

@@ -171,7 +171,7 @@ def calculate_medians(self, epoch: VotingEpoch, signing_policy: SigningPolicy):
             for e, _, s_2 in votes_to_consider:
                 values = s_2.parsed_payload.payload.values
 
-                if len(values) < i:
+                if i >= len(values):
                     continue
 
                 value = values[i]