Rename `#encrypted_attributes` to `#attr_encrypted_encrypted_attributes`

[david-a-wheeler]

Address this Post-install message from attr_encrypted:

WARNING: Using `#encrypted_attributes` is no longer supported. Instead, use `#attr_encrypted_encrypted_attributes` to avoid
  collision with Active Record 7 native encryption.

[andrewfader]

Moot if migrating to it, though