Cron: Cast doing_cron transient to a float.

Cast the `doing_cron` transient value to a float to prevent type errors if the transient is not set (in which case it returns `false`) or another unexpected type.

Props fzhantw, ankitmaru.
Fixes #58471.



git-svn-id: https://develop.svn.wordpress.org/trunk@56553 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/cron.php

@@ -863,7 +863,7 @@ function spawn_cron( $gmt_time = 0 ) {
 	 * Multiple processes on multiple web servers can run this code concurrently,
 	 * this lock attempts to make spawning as atomic as possible.
 	 */
-	$lock = get_transient( 'doing_cron' );
+	$lock = (float) get_transient( 'doing_cron' );
 
 	if ( $lock > $gmt_time + 10 * MINUTE_IN_SECONDS ) {
 		$lock = 0;