Bump line limit for generated_go (#4857)

In some cases (e.g. the Cilium project) the `Code generated by` comment
appears after a license header. This header might be longer than 10
lines which generated_go currently searches for this comment.

Bump the limit to 40 lines (roughly corresponding to the length of the
BSD 4-clause header + some slack) to detect these cases.

Suggested by Paul Chaignon in
cilium/cilium#11326 (comment)

lib/linguist/generated.rb

@@ -302,7 +302,7 @@ def generated_go?
       return false unless extname == '.go'
       return false unless lines.count > 1
 
-      return lines.first(10).any? { |l| l.include? "Code generated by" }
+      return lines.first(40).any? { |l| l.include? "Code generated by" }
     end
 
     PROTOBUF_EXTENSIONS = ['.py', '.java', '.h', '.cc', '.cpp', '.m', '.rb', '.php']