Omit CI when just .md files change, check concurrency

Author: mringler

.github/workflows/ci.yml

@@ -6,8 +6,14 @@ on:
       - 'main'
       - 'develop'
   pull_request:
+    paths-ignore:
+      - '**.md'
   workflow_dispatch:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 env:
   DB_NAME: 'perpl_tests'
   DB_USER: 'perpl'