[6.x] Fix Eloquent user data setting roles and groups as model attributes

[lazerg]

Running php please migrate-dates-to-utc on a site with Eloquent users fails with SQLSTATE[42S22]: Column not found: 1054 Unknown column 'roles' in 'field list'.

The command reads a user's data, converts the date fields, then writes the whole array back through data(). The getter injects roles and groups from their relationship tables, but the setter passes every key through set(), which assigns them straight to the Eloquent model, so the save tries to write columns that don't exist. merge() was fixed the same way in #14526, and UsersController already strips both keys before calling data().

The same crash happens anywhere else data is round-tripped through the setter, such as renaming an asset, which goes through AssetReferenceUpdater.

Fixes #15124