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

@@ -25,7 +25,6 @@ def load_script(**args)
   end
 end
 
-unless ENV['CI']
 context '4.x -> 5.x tag migrator' do
   include Rack::Test::Methods
 
@@ -83,4 +82,3 @@ unless ENV['CI']
     FileUtils.rm_rf(@path)
   end
 end
-end