Ads do not work on clean install till browser restart

[btlechowski]

Description

Fixed after browser restart. Maybe due to seed variation not being enabled.

Found by @Uni-verse

Steps to reproduce

1. Clean install (do not restart)
2. Enable rewards
3. Trigger ads

Actual result

Notification ads, NTT ads and Brave news ads are shown, but there are many error.
Errors:

error	19:41:51.324470+0100	Client	Failed to load data for publisher_state.json: The file “publisher_state.json” couldn’t be opened because there is no such file.
error	19:41:51.941572+0100	Client	Failed to load data for client.json: The file “client.json” couldn’t be opened because there is no such file.
error	19:41:51.941732+0100	Client	Failed to load data for client.json: The file “client.json” couldn’t be opened because there is no such file.
error	19:41:51.942373+0100	Client	Failed to load data for confirmations.json: The file “confirmations.json” couldn’t be opened because there is no such file.
error	19:41:51.943886+0100	Client	Failed to load data for confirmations.json: The file “confirmations.json” couldn’t be opened because there is no such file.
error	19:41:52.004688+0100	Client	Failed to register device with mobile attestation server: <private>
info	19:41:52.832530+0100	Client	[ads] Failed to get signed tokens

Expected result

Ads work.

Reproduces how often

Easily reproduced

Brave version

Reproduced on 1.75.44 on iPhone 13 Pro Max (iOS 17.7)
Reproduced on 1.73.91 on iPhone 13 Pro Max (iOS 17.7)

cc @tmancey @aseren @iambrianfung