docs: fix code typo in for loop (#2209)

Author: aniketmaurya

docs/ko/usage.md

@@ -58,7 +58,7 @@ SDK 는 `request_usage_entries` 에서 각 API 요청의 사용량을 자동으
 ```python
 result = await Runner.run(agent, "What's the weather in Tokyo?")
 
-for request in enumerate(result.context_wrapper.usage.request_usage_entries):
+for i, request in enumerate(result.context_wrapper.usage.request_usage_entries):
     print(f"Request {i + 1}: {request.input_tokens} in, {request.output_tokens} out")
 ```
 

docs/usage.md

@@ -54,7 +54,7 @@ The SDK automatically tracks usage for each API request in `request_usage_entrie
 ```python
 result = await Runner.run(agent, "What's the weather in Tokyo?")
 
-for request in enumerate(result.context_wrapper.usage.request_usage_entries):
+for i, request in enumerate(result.context_wrapper.usage.request_usage_entries):
     print(f"Request {i + 1}: {request.input_tokens} in, {request.output_tokens} out")
 ```
 

docs/zh/usage.md

@@ -58,7 +58,7 @@ SDK 会自动在 `request_usage_entries` 中跟踪每个 API 请求的用量，
 ```python
 result = await Runner.run(agent, "What's the weather in Tokyo?")
 
-for request in enumerate(result.context_wrapper.usage.request_usage_entries):
+for i, request in enumerate(result.context_wrapper.usage.request_usage_entries):
     print(f"Request {i + 1}: {request.input_tokens} in, {request.output_tokens} out")
 ```