Filter classic editor gallery shortcodes

gallery_shortcode_filter.php

<?php

/* filter gallery output*/
add_filter( 'shortcode_atts_gallery', 'my_shortcode_atts_gallery', 10, 4 );
function my_shortcode_atts_gallery( $out, $pairs, $atts, $shortcode ) {
    if ( ! isset( $atts['columns'] )  ) {
        $out['columns'] = 1;
    }
    if ( ! isset( $atts['size'] )  ) {
        $out['size'] = 'full';
    }
    if ( ! isset( $atts['link'] ) ) {
        $out['link'] = 'none';
    }   
    return $out;
}