fix(ci): disable running on schedule

Can't publish backend on Heroky because Heroku has changed Terms of Service

Author: deemp

.github/workflows/ci.yaml

@@ -94,6 +94,6 @@ name: Nix CI
 "on":
   pull_request: {}
   push: {}
-  schedule:
-    - cron: 0 0 * * *
+  # schedule:
+  #  - cron: 0 0 * * *
   workflow_dispatch: {}