Update restraints on PermissionsPolicyDoc

[jonjara]

This restraint is specifically for string types

This will work automatically when removed:

https://github.com/aws-cloudformation/aws-cloudformation-resource-providers-codeartifact/blob/cf76eab182c3c9214a48910022606530116092b6/aws-codeartifact-domain/aws-codeartifact-domain.json#L32

Update for both Repositories and Domains