Show recent avatars from contributor level

Hi there,

I am using this post to show the latest avatars / authors:

https://www.wpbeginner.com/wp-tutorials/how-to-display-an-author-list-with-avatars-in-wordpress-contributors-page/

Have it working fine for alphabetical list of ALL authors.

===

We only want to show 6 avatars, also show contributor accounts only.

How do we rewrite this in functions.php?

Currently:

// function for author avatar list on homepage
function contributors() {
global $wpdb;

$authors = $wpdb->get_results("SELECT ID, user_nicename from $wpdb->users ORDER BY display_name");

foreach($authors as $author) {
echo "<li>";
echo "<a href=\"".get_bloginfo('url')."/?author=";
echo $author->ID;
echo "\">";
echo get_avatar($author->ID);
echo "</a>";
echo "</li>";
}
}