Update publish.yml

Set a cron schedule to run nightly

.github/workflows/publish.yml

@@ -1,6 +1,9 @@
 name: Create and publish a Docker image
 
-on: [push]
+on:
+  push:
+  schedule:
+    - cron: "0 0 * * *"
 
 # Defines two custom environment variables for the workflow.
 # These are used for the Container registry domain, and a name for the Docker image that this workflow builds.
@@ -53,4 +56,4 @@ jobs:
           context: .
           push: true
           tags: ${{ steps.meta.outputs.tags }}
-          labels: ${{ steps.meta.outputs.labels }}
+          labels: ${{ steps.meta.outputs.labels }}