Fix hl_lines offset in observers lesson onFilePublish code block

The highlight range was off by two, highlighting lines 25-28 instead of
23-26. The correct range covers the full onFilePublish method block
(@OverRide, method signature, println, closing brace).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: pinin4fjords

docs/en/docs/side_quests/plugin_development/05_observers.md

@@ -387,7 +387,7 @@ First, update `greet.nf` so the `SAY_HELLO` process publishes its output files:
 
 Add an `onFilePublish` method and the required import to `TaskCounterObserver.groovy`:
 
-```groovy title="nf-greeting/src/main/groovy/training/plugin/TaskCounterObserver.groovy" linenums="1" hl_lines="5 25-28"
+```groovy title="nf-greeting/src/main/groovy/training/plugin/TaskCounterObserver.groovy" linenums="1" hl_lines="5 23-26"
 package training.plugin
 
 import groovy.transform.CompileStatic