Deprecated hook: wpmu_new_blog

The hook wpmu_new_blog was deprecated in WordPress 5.1 and instead wp_insert_site should be used.

The signature also changed from a bunch parameters to a single WP_Site instance.

I don’t know if the code-base supports conditional hooks based on the core version, but here is how Yoast handled the change:
https://github.com/Yoast/wordpress-seo/pull/12320/files

Here’s the relevant line in the code-base:
https://github.com/xwp/stream/blob/e207cf8795542eb73bdce7b80f037ea8e3a22e55/connectors/class-connector-blogs.php#L18