fix(locales): Update ja_JP.ts

[huyikai]

Using the < a-range-picker > component of the Japanese internationalization configuration, when the picker attribute is set to month, the placeholder still displays "日付を選択 (select date)", which is not in line with expectations.
Although you can modify placeholder manually for the time being, you hope to solve this problem fundamentally.
Look at the source code and find that the relevant configuration is missing in the Japanese internationalization configuration. Therefore, it is supplemented and perfected in this pr.

使用日语国际化配置的 <a-range-picker> 组件，picker 属性设置为 month 时，placeholder 仍然显示 "日付を選択(选择日期)" 这不符合预期。

虽然可以暂时手动修改 placeholder ，但希望从根本解决此问题。

查看源代码发现日语国际化配置中缺少相关配置。故在此 pr 中补充完善。

[github-actions]

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