add CHANGELOG for f6e293ec. [ci skip]

actionpack/CHANGELOG.md

+*   Fix regression in functional tests. Responses should have default headers
+    assigned.
+
+    See #18423.
+
+    *Jeremy Kemper*, *Yves Senn*
+
 *   Deprecate AbstractController#skip_action_callback in favor of individual skip_callback methods
     (which can be made to raise an error if no callback was removed).