Fix Lint/Void offences

.rubocop_todo/lint/void.yml

@@ -3,5 +3,4 @@
 Lint/Void:
   Details: grace period
   Exclude:
-    - 'ee/lib/gitlab/llm/ai_message.rb'
     - 'spec/lib/gitlab/import_export/json/streaming_serializer_spec.rb'

ee/lib/gitlab/llm/ai_message.rb

@@ -82,7 +82,7 @@ def slash_command?
       end
 
       def slash_command_prompt?
-        false unless slash_command?
+        return false unless slash_command?
 
         command, _ = slash_command_and_input