fix: do keep rubocop errors for debug when auto-detecting it

Author: doudou

lib/roby/app/rake.rb

@@ -815,7 +815,7 @@ def self.define_rubocop_if_enabled(
             end
 
             def self.detect_rubocop?
-                run_rubocop("--version", out: :close, err: :close)
+                run_rubocop("--version", out: :close)
                 true
             rescue Errno::ENOENT
                 false