Redmine

Thank you for reporting this issue.
I am setting the target version to 6.0.3.

The following patch updates the tests to detect this issue.

diff --git a/test/integration/api_test/custom_fields_test.rb b/test/integration/api_test/custom_fields_test.rb
index 0df56e59a..ca772417a 100644
--- a/test/integration/api_test/custom_fields_test.rb
+++ b/test/integration/api_test/custom_fields_test.rb
@@ -29,6 +29,7 @@ class Redmine::ApiTest::CustomFieldsTest < Redmine::ApiTest::Base
       assert_select 'custom_field' do
         assert_select 'name', :text => 'Database'
         assert_select 'description', :text => 'Select one of the databases'
+        assert_select 'editable', :text => 'true'
         assert_select 'id', :text => '2'
         assert_select 'customized_type', :text => 'issue'
         assert_select 'possible_values[type=array]' do

editable attribute added to the custom fields API response.

Merged to stable branches.