Don't include archived projects when creating group milestones

CHANGELOG

@@ -54,6 +54,7 @@ v 8.13.0 (unreleased)
   - Close todos when accepting merge requests via the API !6486 (tonygambone)
   - Changed Slack service user referencing from full name to username (Sebastian Poxhofer)
   - Add Container Registry on/off status to Admin Area !6638 (the-undefined)
+  - Don't include archived projects when creating group milestones (!4940)
 
 v 8.12.4 (unreleased)
   - Fix type mismatch bug when closing Jira issue

app/views/groups/milestones/new.html.haml

@@ -33,8 +33,8 @@
       .form-group
         = f.label :projects, "Projects", class: "control-label"
         .col-sm-10
-          = f.collection_select :project_ids, @group.projects, :id, :name,
-            { selected: @group.projects.map(&:id) }, multiple: true, class: 'select2'
+          = f.collection_select :project_ids, @group.projects.non_archived, :id, :name,
+            { selected: @group.projects.non_archived.pluck(:id) }, multiple: true, class: 'select2'
 
     .col-md-6
       .form-group