Add an entry in the latest whatsnew rst doc file

Author: prazian

doc/source/whatsnew/v3.0.0.rst

@@ -978,6 +978,7 @@ I/O
 - Bug in :meth:`read_stata` where the missing code for double was not recognised for format versions 105 and prior (:issue:`58149`)
 - Bug in :meth:`set_option` where setting the pandas option ``display.html.use_mathjax`` to ``False`` has no effect (:issue:`59884`)
 - Bug in :meth:`to_csv` where ``quotechar``` is not escaped when ``escapechar`` is not None (:issue:`61407`)
+- 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:`to_excel` where :class:`MultiIndex` columns would be merged to a single row when ``merge_cells=False`` is passed (:issue:`60274`)
 
 Period