Docs: Convert `@see` reference in `wp_checkdate()` DocBlock to `@link`.

Props WiZZarD_.
Fixes #44866.

git-svn-id: https://develop.svn.wordpress.org/trunk@43599 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -5592,7 +5592,7 @@ function wp_is_stream( $path ) {
  *
  * @since 3.5.0
  *
- * @see checkdate()
+ * @link https://secure.php.net/manual/en/function.checkdate.php
  *
  * @param  int    $month       Month number.
  * @param  int    $day         Day number.