Is your enhancement related to a problem? Please describe.

Elasticsearch only allows asc or desc for the sorting, and if the WordPress query has orderby to post__in; the ES query ends with the error No mapping found for [post__in] in order to sort on.  

As the query never ends successfully, to prevent this error, the suggested solution is to never send the request to ES if the orderby is set to post__in. 

Related issue #773

Designs

No response

Describe alternatives you've considered

No response

Code of Conduct

• I agree to follow this project's Code of Conduct