Revert "test_gem_command_manager.rb.

This reverts commit 8aa885c and
cd07c3c.

Author: hsbt

test/rubygems/test_gem_command_manager.rb

@@ -72,7 +72,6 @@ def test_find_command_unknown
   end
 
   def test_find_command_unknown_suggestions
-    omit "randomly fails on ruby/ruby CI" if ENV["GITHUB_REPOSITORY"] == "ruby/ruby"
     e = assert_raise Gem::UnknownCommandError do
       @command_manager.find_command "pish"
     end