docs: add link to Security Advisory on GitHub

Author: kenjis

user_guide_src/source/changelogs/v4.4.7.rst

@@ -14,6 +14,9 @@ Release Date: Unreleased
 SECURITY
 ********
 
+- *Language class DoS Vulnerability* was fixed.
+  See the `Security advisory GHSA-39fp-mqmm-gxj6 <https://github.com/codeigniter4/CodeIgniter4/security/advisories/GHSA-39fp-mqmm-gxj6>`_
+  for more information.
 - **URI Security:** The feature to check if URIs do not contain not permitted
   strings has been added. This check is equivalent to the URI Security found in
   CodeIgniter 3. This is enabled by default, but upgraded users need to add