fix: add the missing abab6.5t-chat model of Minimax

[acelyc111]

Summary

There is a LLM model named abab6.5t-chat in api/core/model_runtime/model_providers/minimax/llm, but it's missing in api/core/model_runtime/model_providers/minimax/llm/llm.py, so if select abab6.5t-chat model and run the application, a KeyError will be threw.

Screenshots

Checklist

Important

Please review the checklist below before submitting your pull request.

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[crazywoola]

cc @laipz8200 @Yeuoly