wip! publish on a schedule, every 5 minutes

currently takes ~3m to run, so should be ok every 5.  the concurrency
group will ensure it doesn't stomp on itself, but it also means if it
starts taking longer than 5m to run then things will start queueing up
and going further out of date since we can't choose to cancel new jobs
just let them go pending.  maybe should address that!

adding ref to the concurrency group ensures we can still run this on PR
branches, etc.

.github/workflows/publish.yaml

@@ -2,6 +2,8 @@
 name: publish
 
 on:
+  schedule:
+    - cron: '*/5 * * * *'
   push:
     branches:
       # XXX FIXME
@@ -15,7 +17,7 @@ permissions:
   id-token: write
 
 concurrency:
-  group: ${{ github.workflow }}
+  group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: false
 
 jobs: