Updates logging.timezone section in migration guide

docs/migration/migrate_8_0.asciidoc

@@ -52,7 +52,18 @@ for example, `logstash-*`.
 ==== Default logging timezone is now the system's timezone
 *Details:* In prior releases the timezone used in logs defaulted to UTC.  We now use the host machine's timezone by default.
 
-*Impact:* To restore the previous behavior, in kibana.yml set `logging.timezone: UTC`.
+*Impact:* To restore the previous behavior, in kibana.yml use the pattern layout, with a date modifier:
+[source,yaml]
+-------------------
+logging:
+  appenders:
+    console:
+      kind: console
+      layout:
+        kind: pattern
+        pattern: "%date{ISO8601_TZ}{UTC}"
+-------------------
+See https://github.com/elastic/kibana/pull/90368 for more details.
 
 [float]
 ==== Responses are never logged by default