Sync date_diff and DateTime::diff return type

This function/method cannot return false.

Author: nikic

ext/date/php_date.stub.php

@@ -238,7 +238,7 @@ public function setTimestamp(int $timestamp) {}
     public function getTimestamp() {}
 
     /**
-     * @return DateInterval|false
+     * @return DateInterval
      * @alias date_diff
      */
     public function diff(DateTimeInterface $targetObject, bool $absolute = false) {}
@@ -291,7 +291,7 @@ public function getOffset() {}
     public function getTimestamp() {}
 
     /**
-     * @return DateInterval|false
+     * @return DateInterval
      * @alias date_diff
      */
     public function diff(DateTimeInterface $targetObject, bool $absolute = false) {}

ext/date/php_date_arginfo.h

@@ -1,5 +1,5 @@
 /* This is a generated file, edit the .stub.php file instead.
- * Stub hash: 339c2c91f38eeaafac6134ac04573243069502f5 */
+ * Stub hash: 880a93d8a3461635447318317869fa7d3d7762dd */
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_MASK_EX(arginfo_strtotime, 0, 1, MAY_BE_LONG|MAY_BE_FALSE)
 	ZEND_ARG_TYPE_INFO(0, datetime, IS_STRING, 0)