Update ftplib.all_errors documentation to match code (#15026)

The documentation doesn't mention the `EOFError` that https://github.com/python/cpython/blob/master/Lib/ftplib.py#L66 includes

Doc/library/ftplib.rst

@@ -144,7 +144,7 @@ The module defines the following items:
    The set of all exceptions (as a tuple) that methods of :class:`FTP`
    instances may raise as a result of problems with the FTP connection (as
    opposed to programming errors made by the caller).  This set includes the
-   four exceptions listed above as well as :exc:`OSError`.
+   four exceptions listed above as well as :exc:`OSError` and :exc:`EOFError`.
 
 
 .. seealso::