Added code to cancel pending deployments on same branch.

This avoids situations where, after creating a template and updating the
polis_url, if the new conversation is small tthan the original, it will
complete it's run much sooner, and get override by the upstream conversation
that was running in the template's initial commit. We must cancel it.

Author: patcon

.github/workflows/deploy.yml

@@ -10,6 +10,11 @@ on:
       - main
   workflow_dispatch:
 
+# Cancel any pending deployment on the same branch.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build:
     # The action is currently tested on ubuntu-latest (Recommended)