Networks and sites: Replace "blog" usage with "site" in docs.

Multisite functions use the term "blog" to refer to what we now call a "site," e.g. `get_current_blog_id()`. These functions are here to stay because of our commitment to backwards compatibility. What we can do is set the documentation straight.

See #35417.


git-svn-id: https://develop.svn.wordpress.org/trunk@36416 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/network/upgrade.php

@@ -92,7 +92,7 @@ switch ( $action ) {
 			 *
 			 * @since MU
 			 *
-			 * @param int $blog_id The id of the blog.
+			 * @param int $blog_id The Site ID.
 			 */
 			do_action( 'wpmu_upgrade_site', $details[ 'blog_id' ] );
 		}