Speed up setup test by not installing docs

This also makes this test consistent with the other tests in this file.

test/rubygems/test_gem_commands_setup_command.rb

@@ -125,6 +125,8 @@ class TestGemCommandsSetupCommand < Gem::TestCase
   end
 
   def test_execute_informs_about_installed_executables
+    @cmd.options[:document] = []
+
     use_ui @ui do
       @cmd.execute
     end