Ensure specs on sorting of issues in API are deterministic on MySQL

CHANGELOG

@@ -18,6 +18,7 @@ v 8.12.0 (unreleased)
   - Use Search::GlobalService.new in the `GET /projects/search/:query` endpoint
   - Fix pagination on user snippets page
   - Fix sorting of issues in API
+  - Ensure specs on sorting of issues in API are deterministic on MySQL
   - Escape search term before passing it to Regexp.new !6241 (winniehell)
   - Fix pinned sidebar behavior in smaller viewports !6169
   - Change merge_error column from string to text type

spec/factories/issues.rb

 FactoryGirl.define do
+  sequence :issue_created_at do |n|
+    4.hours.ago + ( 2 * n ).seconds
+  end
+
   factory :issue do
     title
     author

spec/requests/api/issues_spec.rb

@@ -18,6 +18,7 @@ describe API::API, api: true  do
            project: project,
            state: :closed,
            milestone: milestone,
+           created_at: generate(:issue_created_at),
            updated_at: 3.hours.ago
   end
   let!(:confidential_issue) do
@@ -26,6 +27,7 @@ describe API::API, api: true  do
            project: project,
            author: author,
            assignee: assignee,
+           created_at: generate(:issue_created_at),
            updated_at: 2.hours.ago
   end
   let!(:issue) do
@@ -34,6 +36,7 @@ describe API::API, api: true  do
            assignee: user,
            project: project,
            milestone: milestone,
+           created_at: generate(:issue_created_at),
            updated_at: 1.hour.ago
   end
   let!(:label) do