added WeakReference "PHP 8" version info.

https://github.com/php/php-src/blob/PHP-8.0/Zend/zend_weakrefs_arginfo.h#L38-L40

Author: mumumu

language/predefined/versions.xml

@@ -98,10 +98,10 @@
  <function name="throwable::getprevious" from="PHP 7, PHP 8"/>
  <function name="throwable::__toString" from="PHP 7, PHP 8"/>
 
- <function name="WeakReference" from="PHP 7 &gt;= 7.4.0"/>
- <function name="WeakReference::__construct" from="PHP 7 &gt;= 7.4.0"/>
- <function name="WeakReference::create" from="PHP 7 &gt;= 7.4.0"/>
- <function name="WeakReference::get" from="PHP 7 &gt;= 7.4.0"/>
+ <function name="WeakReference" from="PHP 7 &gt;= 7.4.0, PHP 8"/>
+ <function name="WeakReference::__construct" from="PHP 7 &gt;= 7.4.0, PHP 8"/>
+ <function name="WeakReference::create" from="PHP 7 &gt;= 7.4.0, PHP 8"/>
+ <function name="WeakReference::get" from="PHP 7 &gt;= 7.4.0, PHP 8"/>
  <function name="WeakMap" from="PHP 8"/>
  <function name="WeakMap::__construct" from="PHP 8"/>
  <function name="WeakMap::count" from="PHP 8"/>