Prepend blank line to close message on merge request

- Added an extra new line to the prepend of the Close message

Fixes #21710

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 v 8.12.0 (unreleased)
+  - Prepend blank line to `Closes` message on merge request linked to issue (lukehowell)
   - Filter tags by name !6121
   - Make push events have equal vertical spacing.
   - Add two-factor recovery endpoint to internal API !5510

app/services/merge_requests/build_service.rb

@@ -83,7 +83,7 @@ module MergeRequests
         closes_issue = "Closes ##{iid}"
         if merge_request.description.present?
-          merge_request.description += closes_issue.prepend("\n")
+          merge_request.description += closes_issue.prepend("\n\n")
         else
           merge_request.description = closes_issue
         end

spec/services/merge_requests/build_service_spec.rb

@@ -99,14 +99,14 @@ describe MergeRequests::BuildService, services: true do
         let(:source_branch) { "#{issue.iid}-fix-issue" }
         it 'appends "Closes #$issue-iid" to the description' do
-          expect(merge_request.description).to eq("#{commit_1.safe_message.split(/\n+/, 2).last}\nCloses ##{issue.iid}")
+          expect(merge_request.description).to eq("#{commit_1.safe_message.split(/\n+/, 2).last}\n\nCloses ##{issue.iid}")
         end
         context 'merge request already has a description set' do
           let(:description) { 'Merge request description' }
           it 'appends "Closes #$issue-iid" to the description' do
-            expect(merge_request.description).to eq("#{description}\nCloses ##{issue.iid}")
+            expect(merge_request.description).to eq("#{description}\n\nCloses ##{issue.iid}")
           end
         end