fix(deps): update dependency langchain to ^0.2.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
langchain	^0.1.4 -> ^0.2.0

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[renovate]

⚠️ Artifact update problem

Renovate failed to update an artifact related to this branch. You probably do not want to merge this PR as-is.

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• any of the package files in this branch needs updating, or
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The artifact failure details are included below:

File name: poetry.lock

Updating dependencies
Resolving dependencies...


Because langchain-experimental (0.0.58) depends on langchain (>=0.1.17,<0.2.0)
 and no versions of langchain-experimental match >0.0.58,<0.0.59, langchain-experimental (>=0.0.58,<0.0.59) requires langchain (>=0.1.17,<0.2.0).
So, because gpt-training depends on both langchain (^0.2.0) and langchain-experimental (^0.0.58), version solving failed.