## Summary
- Ensure `email_verified_at` is set when the demo account is created or
already exists but is unverified
- `email_verified_at` is not in the User model's `$fillable` array, so
set it directly on the model instead of via `create()`/`update()`
## Test plan
- [x] Added test that an existing unverified demo user gets verified on
`demo:reset`
- [x] Added assertion that newly created demo user has
`email_verified_at` set
- [x] All 3 demo reset tests pass
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