Some code uses constructs that will fail under Python 3.12

[perllaghu]

I'm testing a plugin for NBGrader, and getting the following errors [backslash wrapping by me]:

..../python3.11/site-packages/nbgrader/nbgraderformat/v1.py:119: DeprecationWarning: typing.io is deprecated, \
import directly from typing instead. typing.io will be removed in Python 3.12.
    def read_v1(source: typing.io.TextIO, as_version: int, **kwargs: typing.Any) -> NotebookNode:

and

..../python3.11/site-packages/nbgrader/api.py:1013: SADeprecationWarning: User-placed attribute Grade.cell_type \
on Mapper[Grade(grade)] is replacing an existing class-bound attribute of the same name.  Behavior is not fully \
defined in this case.  This use is deprecated and will raise an error in a future release
    Grade.cell_type = column_property(

[shreve]

The first one is fixed in nbgrader 0.9.3: 720299d

It looks like the other one should be a simple fix.