php 8 compatibility

Hello,

Thanks for a great plugin!

Just wanted to notify you that I get these errors when running php 8:

[08-Dec-2021 00:28:35 UTC] PHP Deprecated: Required parameter $temp_id follows optional parameter $echo in /var/www/vhosts/richimmobilier.com/httpdocs/wp-content/plugins/wp-email/wp-email.php on line 516
[08-Dec-2021 00:28:35 UTC] PHP Deprecated: Required parameter $temp_id follows optional parameter $echo in /var/www/vhosts/richimmobilier.com/httpdocs/wp-content/plugins/wp-email/wp-email.php on line 557`

Kind regards,

Marcus