fix: exercises.py - handle dict rows in fetchone() for INSERT RETURNING

backend/routers/exercises.py

@@ -401,7 +401,8 @@ def create_exercise(
                 body.visibility, body.status, profile_id, body.club_id,
             )
         )
-        exercise_id = cur.fetchone()[0]
+        row = cur.fetchone()
+        exercise_id = row['id'] if isinstance(row, dict) else row[0]
         conn.commit()
 
         # M:N Relations zuweisen