FSE Change Post Template to Something Other Than a List

The ul/li tags are hard-coded into the render_block_core_post_template() functíon:

$content="";
    while ( $query->have_posts() ) {
        $query->the_post();
        $block_content = (
            new WP_Block(
                $block->parsed_block,
                array(
                    'postType' => get_post_type(),
                    'postId'   => get_the_ID(),
                )
            )
        )->render( array( 'dynamic' => false ) );
        $content      .= "<li>{$block_content}</li>";
    }

    wp_reset_postdata();

    return sprintf(
        '<ul %1$s>%2$s</ul>',
        $wrapper_attributes,
        $content
    );

See here:

https://github.com/WordPress/wordpress-develop/blob/bed9d00fbdac9da08ed13e84186c53a686a1ea78/src/wp-includes/blocks/post-template.php#L69

There would be a hacky way to modify the output via the render_block filter, but it might be better to work through the problem via CSS instead.