Add assertion for extra_data type narrowing in tests

Added `assert self.extra_data is not None` after assignment in
TestUserSocialAuth.__init__. This narrows the type from
`dict[str, Any] | None` (from base class) to `dict[str, Any]`
for the type checker, eliminating 76 type errors where tests
subscript extra_data.

The assertion is always true since line 90 assigns `extra_data or {}`,
ensuring extra_data is never None in tests.

Co-authored-by: nijel <[email protected]>

Author: Copilot

social_core/tests/models.py

@@ -88,6 +88,8 @@ def __init__(self, user: User, provider, uid, extra_data=None) -> None:
         self.provider = provider
         self.uid = uid
         self.extra_data = extra_data or {}
+        # Type narrowing: extra_data is always a dict in tests, never None
+        assert self.extra_data is not None
         self.user.social.append(self)
         TestUserSocialAuth.cache_by_uid[uid] = self