Run test_migrate tests on CI

Now that we've resolved the issue with the invalid git repository in the
parent commit, we can run all of the tests in our CI environment.

test/test_migrate.rb

@@ -25,8 +25,7 @@ def load_script(**args)
   end
 end
 
-unless ENV['CI']
+context '4.x -> 5.x tag migrator' do
-  context '4.x -> 5.x tag migrator' do
   include Rack::Test::Methods
 
   setup do
@@ -82,5 +81,4 @@ unless ENV['CI']
   teardown do
     FileUtils.rm_rf(@path)
   end
-  end
 end