Format the exception part of the traceback.
The return value is a generator of strings, each ending in a newline.
Generator yields the exception message.
For :exc:`SyntaxError` exceptions, it
also yields (before the exception message)
several lines that (when printed)
display detailed information about where the syntax error occurred.
Following the message, generator also yields
all the exception's ``__notes__``.
When *show_group* is ``True``, and the exception is an instance of
:exc:`BaseExceptionGroup`, the nested exceptions are included as
well, recursively, with indentation relative to their nesting depth.