fix: fix initialization of I18N weekdays

Description

As discussed in https://github.com/vaadin/flow-components/issues/6353#issuecomment-2175966174, the result of DateFormatSymbols.getWeekdays and DateFormatSymbols.getShortWeekdays returns 8 items instead of 7.

For example:

System.out.println(String.join(",", dfs.getWeekdays()));
System.out.println(String.join(",", dfs.getShortWeekdays()));

Prints:

,Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday
,Sun,Mon,Tue,Wed,Thu,Fri,Sat

Fixes #329

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