Update CI Config to fix randomly failing tests in Redmine 5.1.2

.github/workflows/5_1_2.yml

@@ -89,8 +89,9 @@ jobs:
       - name: Prepare Redmine source
         working-directory: redmine
         run: |
-          # Add missing :groups_users fixture to API tests
+          # Add missing fixtures to API tests
           sed -i='' 's/^  fixtures :users/&, :groups_users/' test/integration/api_test/users_test.rb # TODO: remove next line when fixed in Redmine core
+          sed -i='' 's/^  fixtures(/&:user_preferences,/' test/integration/api_test/issues_test.rb # TODO: remove next line when fixed in Redmine core
           # Fix routes broken by Redmine core plugins tests
           rm -f test/integration/routing/plugins_test.rb # Fix routing tests # TODO Remove this line when https://www.redmine.org/issues/38707 is fixed
           sed -i '/rubocop/d' Gemfile