Only suggest adding livecheck it auto-detection fails.

Library/Homebrew/cask/audit.rb

@@ -316,6 +316,7 @@ module Cask
       case cask.url.to_s
       when %r{sourceforge.net/(\S+)}
         return if cask.version.latest?
+        return unless online?
 
         add_error "Download is hosted on SourceForge, #{add_livecheck}"
       when %r{dl.devmate.com/(\S+)}

Library/Homebrew/test/cask/audit_spec.rb

@@ -630,6 +630,7 @@ describe Cask::Audit, :cask do
 
       context "when the download is hosted on SourceForge and does not have a livecheck" do
         let(:cask_token) { "sourceforge-correct-url-format" }
+        let(:online) { true }
 
         it { is_expected.to fail_with(message) }
       end