Configure CI workflow to handle concurrent releases

**As a** platform engineer
**I want** our deployment process for our app repos to handle concurrent releases
**so that** we avoid issues with incorrect ordering of releases

alphagov/govuk-infrastructure#2123

Author: MuriloDalRi

.github/workflows/ci.yml

@@ -7,6 +7,10 @@ on:
       - main
   pull_request:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.repository }}-${{ github.ref_name }}
+  cancel-in-progress: false
+
 jobs:
   test:
     name: Test