Revoke GH clone token after `post_checkout`

[humitos]

Currently, the GH clone token auto expires after 1h. We can lower down that time limit by revoking the token immediately after using it.

We should revoke it after post_checkout because the user sometimes unshallow the repository at this point and needs the token for that. Also, we should probably revoke it after using it from SyncRepositoryTask as well.

Reference: https://readthedocs.slack.com/archives/C04SS8XNB6K/p1786989086111929