fix PR URL in changelog (elastic#4655)

Author: fearful-symmetry

packages/log/changelog.yml

@@ -3,7 +3,7 @@
   changes:
     - description: Add custom logs and processors
       type: enhancement
-      link: https://github.com/elastic/integrations/pull/2538
+      link: https://github.com/elastic/integrations/pull/4568
 - version: "1.0.0"
   changes:
     - description: Release Custom Logs as GA