GitHub username in Accounts menu does not update after renaming the account on github.com

Does this issue occur when all extensions are disabled?: Yes/No

- VS Code Version:
- OS Version:

Does this issue occur when all extensions are disabled?: Yes

Steps to Reproduce:

1. Sign in to GitHub in VS Code via the Accounts menu.
2. On github.com, change the account's username (Settings > Account > Change username).
3. Return to VS Code and open the Accounts menu.

Expected: the Accounts menu reflects the new username.

Actual: the old username is still displayed. It persists across a window
reload and a full restart of VS Code. Signing out and signing back in with
the same account does not refresh it either.

Additional notes:
- Authentication itself still works, so the cached account label appears to
be stored separately from the session rather than being re-fetched.