MAINTAINERS: update path for utest of serial_v2

[unicornx]

Fixes: 3b97667 ("utest: serial: move from examples to components/drivers/serial")

修改 serial_v2 的 utest 代码路径后需要同步修改 MAINTAINERS 文件信息。

[github-actions]

👋 感谢您对 RT-Thread 的贡献！Thank you for your contribution to RT-Thread!

为确保代码符合 RT-Thread 的编码规范，请在你的仓库中执行以下步骤运行代码格式化工作流（如果格式化CI运行失败）。
To ensure your code complies with RT-Thread's coding style, please run the code formatting workflow by following the steps below (If the formatting of CI fails to run).

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🛠 操作步骤 | Steps

1. 前往 Actions 页面 | Go to the Actions page
   点击进入工作流 → | Click to open workflow →

2. 点击 Run workflow | Click Run workflow

• 设置需排除的文件/目录（目录请以"/"结尾）
  Set files/directories to exclude (directories should end with "/")
• 将目标分支设置为 \ Set the target branch to：dev-fix-maintainer-serial-utest
• 设置PR number为 \ Set the PR number to：10811

3. 等待工作流完成 | Wait for the workflow to complete
   格式化后的代码将自动推送至你的分支。
   The formatted code will be automatically pushed to your branch.

完成后，提交将自动更新至 dev-fix-maintainer-serial-utest 分支，关联的 Pull Request 也会同步更新。
Once completed, commits will be pushed to the dev-fix-maintainer-serial-utest branch automatically, and the related Pull Request will be updated.

如有问题欢迎联系我们，再次感谢您的贡献！💐
If you have any questions, feel free to reach out. Thanks again for your contribution!

[github-actions]

📌 Code Review Assignment

🏷️ Tag: maintainers

Reviewers: @Rbb666 @kurisaW

Changed Files (Click to expand)

• MAINTAINERS

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📊 Current Review Status (Last Updated: 2025-10-14 14:36 CST)

• ⌛ @Rbb666 Pending Review
• ⌛ @kurisaW Pending Review

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📝 Review Instructions

1. 维护者可以通过单击此处来刷新审查状态: 🔄 刷新状态
   Maintainers can refresh the review status by clicking here: 🔄 Refresh Status

2. 确认审核通过后评论 LGTM/lgtm
   Comment LGTM/lgtm after confirming approval

3. PR合并前需至少一位维护者确认
   PR must be confirmed by at least one maintainer before merging

ℹ️ 刷新CI状态操作需要具备仓库写入权限。
ℹ️ Refresh CI status operation requires repository Write permission.

[unicornx]

@Ryan-CW-Code 请 review

[Ryan-CW-Code]

Thanks