IrreversibleError when migrating app zero for a new DB

[raratiru]

Expected behaviour

In a newly created and migrated database:
./manage.py migrate <my_custom_user_app> zero to reverse its migrations.

Actual behaviour

Receiving the error:

  Rendering model states... DONE
  Unapplying social_django.0015_rename_extra_data_new_usersocialauth_extra_data... OK
  Unapplying social_django.0014_remove_usersocialauth_extra_data... OK
  Unapplying social_django.0013_migrate_extra_data...Traceback (most recent call last):
  File "/project-home/./manage.py", line 24, in <module>
    main()
  File "/project-home/./manage.py", line 20, in main
    execute_from_command_line(sys.argv)
  File "/project-home/.venv/lib/python3.11/site-packages/django/core/management/__init__.py", line 442, in execute_from_command_line
    utility.execute()
  File "/project-home/.venv/lib/python3.11/site-packages/django/core/management/__init__.py", line 436, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/project-home/.venv/lib/python3.11/site-packages/django/core/management/base.py", line 412, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/project-home/.venv/lib/python3.11/site-packages/django/core/management/base.py", line 458, in execute
    output = self.handle(*args, **options)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/project-home/.venv/lib/python3.11/site-packages/django/core/management/base.py", line 106, in wrapper
    res = handle_func(*args, **kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/project-home/.venv/lib/python3.11/site-packages/django/core/management/commands/migrate.py", line 356, in handle
    post_migrate_state = executor.migrate(
                         ^^^^^^^^^^^^^^^^^
  File "/project-home/.venv/lib/python3.11/site-packages/django/db/migrations/executor.py", line 141, in migrate
    state = self._migrate_all_backwards(plan, full_plan, fake=fake)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/project-home/.venv/lib/python3.11/site-packages/django/db/migrations/executor.py", line 219, in _migrate_all_backwards
    self.unapply_migration(states[migration], migration, fake=fake)
  File "/project-home/.venv/lib/python3.11/site-packages/django/db/migrations/executor.py", line 279, in unapply_migration
    state = migration.unapply(state, schema_editor)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/project-home/.venv/lib/python3.11/site-packages/django/db/migrations/migration.py", line 159, in unapply
    raise IrreversibleError(
django.db.migrations.exceptions.IrreversibleError: Operation <RunPython <function migrate_json_field at 0x7fc13a366ca0> elidable=True> in social_django.0013_migrate_extra_data is not reversible

What are the steps to reproduce this issue?

Input clear steps to reproduce the issue for a maintainer.

1. Install the app
2. Configure as per the docs:

SOCIAL_AUTH_JSONFIELD_ENABLED = True  # This can also be False, the error remains

AUTHENTICATION_BACKENDS = (
    "social_core.backends.github.GithubOAuth2",
    "django.contrib.auth.backends.ModelBackend",
)

TEMPLATES[0]["OPTIONS"]["context_processors"] += [
    "social_django.context_processors.backends",
    "social_django.context_processors.login_redirect",
]

SOCIAL_AUTH_PIPELINE = (
    'social_core.pipeline.social_auth.social_uid',
    'social_core.pipeline.social_auth.social_user',
    'social_core.pipeline.user.get_username',
    'social_core.pipeline.user.create_user',
    'social_core.pipeline.social_auth.associate_user',
)

SOCIAL_AUTH_ADMIN_USER_SEARCH_FIELDS = ('username',)

3. `./manage.py migrate
4. `./manage.py migrate <my_user_app> zero

[nijel]

Migrations in #465 are not reversible. If you think it's worth addressing, patches are welcome.