feat: add concurrency control to CI workflow

Only one workflow runs at a time per branch. New runs queue instead of
running in parallel, ensuring deployments happen in order.

Author: chriswydra

.github/workflows/landcare-ci.yml

@@ -13,6 +13,10 @@ on:
   push:
     branches: [metaspace]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: false
+
 jobs:
   build:
     uses: manaakiwhenua/github-workflows/.github/workflows/docker-build.yml@main