fix(Modal): 弹窗圆角

[CaedmonW]

这个 PR 做了什么? (简要描述所做更改)

Modal下边框圆角缺失

这个 PR 是什么类型? (至少选择一个)

• [x] 错误修复(Bugfix) fix #{issue id}
• [ ] 新功能(Feature) resolve #{issue id}
• [ ] 代码重构(Refactor)
• [ ] 文档修改(Docs)
• [ ] 代码风格更新(Code style update)
• [ ] 类型描述更新(TypeScript definition update)
• [ ] 其他，请描述(Other, please describe):

这个 PR 涉及以下平台:

• [ ] 未涉及平台修改
• [x] 所有小程序
• [ ] 微信小程序
• [ ] 支付宝小程序
• [ ] 百度小程序
• [ ] 字节跳动小程序
• [ ] QQ 轻应用
• [ ] 京东小程序
• [ ] 快应用平台（QuickApp）
• [x] Web 平台（H5）
• [ ] 移动端（React-Native）

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: e443d98171c731dd64278b63a6299c2004859b51

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

| Name | Type | | ------ | ----- | | ossaui | Patch |

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Name	Status	Preview	Updated
ossa-demo	✅ Ready (Inspect)	Visit Preview	Dec 20, 2022 at 2:16PM (UTC)

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| Name | Status | Preview | Updated | | :--- | :----- | :------ | :------ | | **ossa-doc** | ⬜️ Ignored ([Inspect](https://vercel.com/ossa/ossa-doc/4MbpGZSwmB6ccHHfuzTNejFHFugF)) | | Dec 20, 2022 at 2:16PM (UTC) |