fix(calendar): respect locale prop in month dropdown format

[ikku47]

fix(calendar): respect locale prop in month dropdown format

Previously, the month dropdown formatter was hardcoded to use "default" locale,
ignoring the locale prop passed to the Calendar component. This fix ensures
that when a locale is provided via props.locale?.code, it is used for
formatting the month name in the dropdown, falling back to "default" if no
locale is specified.

This change improves internationalization support by allowing the calendar
to display month names in the correct language based on the provided locale.

Fixes: Month dropdown always displaying in default locale regardless of locale prop

[vercel]

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