fix: update expected Etherscan message

[DanielSchiavini]

What I did

• Updated the expected rate limit message
• Ethercan can return one of:
  • {'status': '0', 'message': 'NOTOK', 'result': 'Max calls per sec rate limit reached (X/sec)'} example
  • {'status': '0', 'message': 'NOTOK', 'result': 'Max rate limit reached'} (existing code)
  • {'status': '0', 'message': 'NOTOK', 'result': 'Max rate limit reached, please use API Key for higher rate limit'} (reference)

How I did it

• Checking the status of the response
• Checking the error message

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