fix: add reference to PR number

Author: ppkarwasz

…og/.2.x.x/refactor_manager_factories.xml ….x.x/3968_refactor_manager_factories.xmlsrc/changelog/.2.x.x/refactor_manager_factories.xml renamed to src/changelog/.2.x.x/3968_refactor_manager_factories.xml src/changelog/.2.x.x/refactor_manager_factories.xml renamed to src/changelog/.2.x.x/3968_refactor_manager_factories.xml

@@ -5,6 +5,7 @@
            https://logging.apache.org/xml/ns
            https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
        type="changed">
+    <issue id="3968" link="https://github.com/apache/logging-log4j2/pull/3968"/>
     <description format="asciidoc">
         Simplify file manager registry factory methods by removing unnecessary boilerplate code.
     </description>