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You can check the value of the post_status query variable and make sure that it's set to trash:

function wpse239286_trash_column( $columns ) {

    // Bail if we're not looking at trash.
    $status = get_query_var( 'post_status' );
    if ( 'trash' !== $status ) {
        return $columns;
    }

    return array_merge( $columns, 
        array( 'trash_column' => __( 'Trash Column', 'text-domain' ) )
    );
}
add_filter( 'manage_posts_columns' , 'wpse239286_trash_column' );
add_filter( 'manage_pages_columns' , 'wpse239286_trash_column' );