默认日期选择，切换为月份日期不对。

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Version

4.2.3

Environment

Vue

Reproduction link

Steps to reproduce

参考codesandbox代码片段

What is expected?

模式为选择月份时，选择月份后应该返回这样格式，例如选择1月到9月返回值应该是2024-01-01~2024-09-30。

现在是，默认时间为2024-05-12 ~ 2024-09-15，切换为月份选择后返回值是2024-01-12 ~ 2024-09-12。

What is actually happening?