Update tiktoken to use gpt-4o

[kazuki-ida]

Hi,

OpenAI announced GPT-4o today. So, tiktoken in pr-agent needs to be updated to version 0.7.0 in order to use this model, according to the tiktoken history.

Reference: openai/tiktoken@9d01e56

Thank you!

[mrT23]

thanks, i think this addressed that
#901

[kazuki-ida]

That's right.
Thank you for the quick response!

I will continue to use the wonderful product, pr-agent.