Update UPGRADING for proc_get_status() and proc_close() change

Author: nielsdos

UPGRADING

@@ -24,6 +24,10 @@ PHP 8.3 UPGRADE NOTES
     Error when using more than
     `zend.max_allowed_stack_size-zend.reserved_stack_size` bytes of stack
     (`fiber.stack_size-zend.reserved_stack_size` for fibers).
+  . Executing proc_get_status() multiple times will now always return the right
+    value. Previously, only the first call of the function returned the right
+    value. Executing proc_close() after proc_get_status() will now also return
+    the right exit code. Previously this would return -1.
 
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 2. New Features