Date/Time: Cast extracted strings to integers in wp_resolve_post_date().

`wp_resolve_post_date()` extracts year/month/day from a post date (which is a string) and passes it to `wp_checkdate` (and from there to `checkdate()`), which requires `int`s.

Casting the strings to integers avoids PHP notices due to incorrect argument types.

Props hilayt24.
Fixes #54186

git-svn-id: https://develop.svn.wordpress.org/trunk@54126 602fd350-edb4-49c9-b593-d223f7449a82

Author: swissspidy

src/wp-includes/post.php

@@ -4945,9 +4945,9 @@ function wp_resolve_post_date( $post_date = '', $post_date_gmt = '' ) {
 	}
 
 	// Validate the date.
-	$month = substr( $post_date, 5, 2 );
-	$day   = substr( $post_date, 8, 2 );
-	$year  = substr( $post_date, 0, 4 );
+	$month = (int) substr( $post_date, 5, 2 );
+	$day   = (int) substr( $post_date, 8, 2 );
+	$year  = (int) substr( $post_date, 0, 4 );
 
 	$valid_date = wp_checkdate( $month, $day, $year, $post_date );