UPGRADING: Fix parameter name in bzcompress work_factor param

Follow-up to phpGH-16108, to add the `$` sign to the `work_factor`
paremter mention in the `UPGRADING` file.

Author: Ayesh

UPGRADING

@@ -22,7 +22,7 @@ PHP 8.5 UPGRADE NOTES
 - BZ2:
   . bzcompress() now throws a ValueError when $block_size is not between
     1 and 9.
-  . bzcompress() now throws a ValueError when work_factor is not between
+  . bzcompress() now throws a ValueError when $work_factor is not between
     0 and 250.
 
 - LDAP: