Daylight savings time is not taken into account for align_date_to_month

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When a date is aligned with the beginning/end of a month, the resulting date keeps the initial timezone, not taking daylight savings time (DST) into account.

For example, if align_date_to_month(date, 'Europe/Zurich', 'up') is run against October 1st 2020, the resulting date has a timezone object that thinks it is part of daylight savings time, even though that changed on October 26.

To illustrate the issue I wrote a test. See:
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