[4.x] Fix EloquentQueryBuilder orderby bug

[duncanmcclean]

This pull request fixes an issue with the recently introduced EloquentQueryBuilder@enforceOrderBy method, where it was trying to access the query property on the Eloquent query builder instance.

However, that property is protected so it errored so couldn't be accessed by the __get method inside Eloquent.

Stack trace:

Exception: Property [query] does not exist on the Eloquent builder instance.

/home/runner/work/eloquent-driver/eloquent-driver/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Builder.php:1943
/home/runner/work/eloquent-driver/eloquent-driver/vendor/statamic/cms/src/Query/EloquentQueryBuilder.php:514
/home/runner/work/eloquent-driver/eloquent-driver/vendor/statamic/cms/src/Query/EloquentQueryBuilder.php:488
/home/runner/work/eloquent-driver/eloquent-driver/vendor/statamic/cms/src/Search/Searchables/Entries.php:34
/home/runner/work/eloquent-driver/eloquent-driver/vendor/statamic/cms/src/Search/Searchables.php:51

This PR fixes that issue by calling the getQuery method on the builder instead of calling the query property directly.

Caused by #9956.