WordPress search only posts when viewing posts

functions;php

function gg_postssearch($query) {
 if( is_single( 'post' ) || is_post_type_archive( 'post' ) {
  if( $query->is_search ) {
   $query->set( 'post_type', 'post' );
  }
  return $query;
 }
}
add_filter( 'pre_get_posts',' gg_postssearch' );