Coding Standards: Fix WPCS issues in `wp-includes/sitemaps/`.

Some of these were not caught when running `composer lint:errors`, but are fixed when running `phpcbf` directly.

Follow-up to [48072], [48080].

See #49542, #50117.
Built from https://develop.svn.wordpress.org/trunk@48081


git-svn-id: https://core.svn.wordpress.org/trunk@47848 1a063a9b-81f0-0310-95a4-ce76da25c4cd