fix: update current year calculation to use isocalendar

src/weekly_strava_stats/storage/week_stats_storage.py

@@ -57,7 +57,7 @@ def load_weekly_stats(self, relative_week_number: int) -> Optional[WeekStats]:
             Optional[StravaStats]: The stats for the requested week. None if the stats are not found.
         """
         now = datetime.now()
-        current_year = now.year
+        current_year = now.isocalendar()[0]
         current_week_number = now.isocalendar()[1]
 
         target_week_number = current_week_number + relative_week_number