Does not work with Pillow 10.1, ImageFile.mode can no longer be set directly

[ran404]

Describe the bug

Does not work with Pillow 10.1. The attribute ImageFile.mode can no longer be set directly.

This is the same issue as: imageio/imageio#1044

I can get it work by monkeypatching the HeifImageFile._open function, changing the line:

self.mode = heif_file.mode

to

self._mode = heif_file.mode

but would be good to have a proper fix.

Steps to reproduce

import HeifImagePlugin
from PIL import Image, ImageOps

with Image.open('some-heic-file.heic') as image:
    # raises exception here

Code / screenshots

  File "/opt/venvs/python/lib/python3.11/site-packages/PIL/Image.py", line 3284, in open
    im = _open_core(fp, filename, prefix, formats)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/venvs/python/lib/python3.11/site-packages/PIL/Image.py", line 3270, in _open_core
    im = factory(fp, filename)
         ^^^^^^^^^^^^^^^^^^^^^
  File "/opt/venvs/python/lib/python3.11/site-packages/PIL/ImageFile.py", line 117, in __init__
    self._open()
  File "/opt/venvs/python/lib/python3.11/site-packages/HeifImagePlugin.py", line 117, in _open
    self.mode = heif_file.mode
    ^^^^^^^^^
AttributeError: property 'mode' of 'HeifImageFile' object has no setter

Environment

• Library version: heif-image-plugin==0.6.0
• Language/framework version: Python 3.11.5
• OS version: CentOS 7.9