Pull Request Checklist

Thank you for taking the time to improve Arrow! Before submitting your pull request, please check all appropriate boxes:

• 🧪 Added tests for changed code.
• 🛠️ All tests pass when run locally (run tox or make test to find out!).
• 🧹 All linting checks pass when run locally (run tox -e lint or make lint to find out!).
• 📚 Updated documentation for changed code.
• ⏩ Code is up-to-date with the master branch.

If you have any questions about your code changes or any of the points above, please submit your questions along with the pull request and we will try our best to help!

Description of Changes

Bug Fix

• Fixed the time zone calculation error in the shift() method during DST transitions.
• Original issue: Performing relativedelta operations directly on localized time caused errors during DST transition points.
• New solution: Convert times with time zones to UTC for calculations, then convert them back to the original time zone.

Code Changes

# Original code (problematic code)
current = self._datetime + relativedelta(**relative_kwargs)
# Modified code (fixed code)
original_tz = self.tzinfo
if self._datetime.tzinfo is not None:
 utc_dt = self._datetime.astimezone(dateutil_tz.UTC)
 current = utc_dt + relativedelta(**relative_kwargs)
 current = current.astimezone(original_tz)
else:
 current = self._datetime + relativedelta(**relative_kwargs)