refactor: update the return type of getConnection()

[shalomabitan]

Using the package with phpstan I was getting an error when attempting to run this code

   public static function refreshIndex(): void
   {
       /** @var static $instance */
       $instance = new static();
       $index = $instance->getIndex();

       try {
           $client = $instance->getConnection()->getClient();
           $client?->indices()?->refresh(['index' => $index]);
       } catch (Throwable $th) {
           logger()->error('Failed to refresh index', ['index' => $index, 'error' => $th->getMessage()]);
       }
   } 

The error phpstan was throwing was

 ------ ----------------------------------------------------------------------------------------------
  Line   app/Traits/Models/OnElasticsearchConnection.php (in context of class App\Models\Search\Lead)
 ------ ----------------------------------------------------------------------------------------------
  29     Cannot call method getClient() on string.
 ------ ----------------------------------------------------------------------------------------------

After digging it was found that the docblock in the src/Eloquent/Docs/ModelDocs.php is incorrectly claiming a string will be returned and not the correct return type of use PDPhilip\Elasticsearch\Connection;

[pdphilip]

Thanks @shalomabitan, we're in the process of rebuilding the package for v5 but will review this for v4 anyway when we get there.