Current user should be nil to prevent ActiveJob::DeserializationError errors in tests.

git-svn-id: http://svn.redmine.org/redmine/trunk@17688 e93f8b46-1217-0410-a6f0-8f06a7374b81

test/unit/custom_field_test.rb

            :trackers, :issue_statuses,
            :issues
 
+  def setup
+    User.current = nil
+  end
+
   def test_create
     field = UserCustomField.new(:name => 'Money money money', :field_format => 'float')
     assert field.save