[rubygems/rubygems] Fix Bundler daily CI

There is another place artifice usage was making the copy of vendored
http in ruby-core be loaded instead of the one under test.

Remove unnecessary usage of artifice.

rubygems/rubygems@d2488199b0

spec/bundler/commands/update_spec.rb

@@ -1380,7 +1380,7 @@
       build_bundler "999.0.0"
     end
 
-    install_gemfile <<-G
+    install_gemfile <<-G, artifice: nil, env: { "BUNDLER_IGNORE_DEFAULT_GEM" => "true" }
       source "#{file_uri_for(gem_repo4)}"
       gem "rack"
     G