fix: 知识库 QA 导入无法选择 md 和 html 文件

[xavierxcn]

知识库-导入-QA 中提示可以选择 md 和 html 文件，但是确无法选择 md 和 html 文件。是因为 QA.tsx中定义的fileExtension变量少写了一个逗号，我加上了这个逗号。

[sweep-ai-deprecated[bot]]

Apply Sweep Rules to your PR?

• [ ] Apply: All new business logic should have corresponding unit tests.
• [ ] Apply: Refactor large functions to be more modular.
• [ ] Apply: Add docstrings to all functions and file headers.

[cla-assistant[bot]]

All committers have signed the CLA.

[xinggonglie]

docker compose部署，还没有修改

[c121914yu]

Bot detected the issue body's language is not English, translate it automatically. 👯👭🏻🧑‍🤝‍🧑👫🧑🏿‍🤝‍🧑🏻👩🏾‍🤝‍👨🏿👬🏿

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Docker compose deployment, not modified yet