Coding Standards: Remove unused return value for WP_Object_Cache::__set().

This resolves a WPCS warning:
{{{
Assignments must be the first block of code on a line
}}}

Note: This is enforced by PHPCS 3.10.3.

Follow-up to [28521], [29146].

Props jrf.
See #62076, #61607.

git-svn-id: https://develop.svn.wordpress.org/trunk@59066 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-includes/class-wp-object-cache.php

@@ -101,10 +101,9 @@ public function __get( $name ) {
 	 *
 	 * @param string $name  Property to set.
 	 * @param mixed  $value Property value.
-	 * @return mixed Newly-set property.
 	 */
 	public function __set( $name, $value ) {
-		return $this->$name = $value;
+		$this->$name = $value;
 	}
 
 	/**