Update dependency ruby-openai to v5.1.0

[renovate[bot]]

This PR contains the following updates:

Package	Update	Change
ruby-openai (changelog)	minor	'5.0.0' -> '5.1.0'

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Release Notes

alexrudall/ruby-openai (ruby-openai)

### [`v5.1.0`](https://togithub.com/alexrudall/ruby-openai/blob/HEAD/CHANGELOG.md#510---2023-08-20) [Compare Source](https://togithub.com/alexrudall/ruby-openai/compare/v5.0.0...v5.1.0) ##### Added - Added rough_token_count to estimate tokens in a string according to OpenAI's "rules of thumb". Thank you to [@​jamiemccarthy](https://togithub.com/jamiemccarthy) for the idea and implementation!

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Configuration

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[yegor256]

@rultor please, try to merge, since 1 checks have passed

[rultor]

@rultor please, try to merge, since 1 checks have passed

@yegor256 OK, I'll try to merge now. You can check the progress of the merge here

[rultor]

@rultor please, try to merge, since 1 checks have passed

@yegor256 Done! FYI, the full log is here (took me 25min)