Fix unpermitted params warnings in non-batched GraphQL queries

What does this MR do and why?

Previously when the client sent through a non-multiplex query, the #multiplex? check led to Unpermitted parameters warnings being logged in development, as it performed the check through permitted_params. In the case where the check should return false, we'd see the warnings.

This changes #multiplex? to avoid those errors.

There should be no functional changes.

How to set up and validate locally

Tail your development log:

tail -f log/development.log

On master branch locally, make a GraphQL query (you can use /-/graphql-explorer):

{
  currentUser {
    id
  }
}

You should see logged:

Unpermitted parameters: :query, :variables, :graphql
Unpermitted parameters: :query, :variables, :graphql

On this branch, the same query should not produce those errors.

MR acceptance checklist

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