Cancel all but the most recent run on the current branch/PR (#12)

This seems overkill for a 2min job, but I guess they all help

.github/workflows/linting.yml

@@ -7,6 +7,12 @@ on:
       - "renovate/**"
   pull_request:
 
+concurrency:
+  cancel-in-progress: true
+  group: >-
+    ${{ github.workflow }}-
+    ${{ github.event.pull_request.number || github.ref }}
+
 jobs:
   linting:
     runs-on: ubuntu-latest