use constant for dictionary key for chain_of_thought

Author: phelps-sg

llm_cooperation/experiments/dilemma.py

@@ -182,7 +182,7 @@ def payout(amount: int) -> str:
         return f"${amount}.00"
 
     def round_instructions() -> str:
-        if participant["chain_of_thought"]:
+        if participant[CONDITION_CHAIN_OF_THOUGHT]:
             return f"""
 For each round, give your answer in the format below on two separate lines:
 Explanation: [why I made my choice]