Add an entry in the latest whatsnew rst doc file

Author: prazian

doc/source/whatsnew/v3.0.0.rst

@@ -953,6 +953,7 @@ I/O
 - Bug in :meth:`DataFrame._repr_html_` which ignored the ``"display.float_format"`` option (:issue:`59876`)
 - Bug in :meth:`DataFrame.from_records` ignoring ``columns`` and ``index`` parameters when ``data`` is an empty iterator and ``nrows=0``. (:issue:`61140`)
 - Bug in :meth:`DataFrame.from_records` where ``columns`` parameter with numpy structured array was not reordering and filtering out the columns (:issue:`59717`)
+- Bug in :meth:`DataFrame.to_csv` / :meth:`Series.to_csv` formatting tz-aware datetimes (microseconds dropped, offset lacked colon); now consistently emits ``YYYY-MM-DD HH:MM:SS.ffffff+HH:MM`` when ``date_format=None``. (:issue:`62111`)
 - Bug in :meth:`DataFrame.to_dict` raises unnecessary ``UserWarning`` when columns are not unique and ``orient='tight'``. (:issue:`58281`)
 - Bug in :meth:`DataFrame.to_excel` when writing empty :class:`DataFrame` with :class:`MultiIndex` on both axes (:issue:`57696`)
 - Bug in :meth:`DataFrame.to_excel` where the :class:`MultiIndex` index with a period level was not a date (:issue:`60099`)