Only log error message after retry fails

What does this MR do and why?

Scenarios

• First attempt fails (with files content) --> Log review_merge_request_retry_without_content
• Retry fails (without files content) --> Log review_merge_request_llm_response_received with error message
• Any success (with/without files content) --> Log review_merge_request_llm_response_received with input / output tokens

So, review_merge_request_llm_response_received with error message would indicate real number of LLM request failures.

MR acceptance checklist

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Related to #510266 (closed)