Wagtail 63 compatibility

[nickmoreton]

This pull request introduces changes to support new versions of Python and Wagtail in the project.

Support for new Python and Wagtail versions:

• .github/workflows/test.yml: Added Python 3.13 to the matrix of Python versions for testing.
• tox.ini: Added Python 3.13 and Wagtail 6.2, 6.3 to the testing environments. Included dependencies for Django 5.1 and Wagtail 6.2, 6.3. [1] [2]

Conditional imports for Wagtail versions:

• src/wagtail_bynder/views/document.py: Added conditional imports and class definitions to support Wagtail versions below and above 6.3. [1] [2] [3]
• src/wagtail_bynder/views/image.py: Added conditional imports and class definitions to support Wagtail versions below and above 6.3. [1] [2] [3]

[ababic]

Thanks for this @nickmoreton. The coverage job failure should have been addressed in main now, so this should be good after a rebase :)