Update nightly-build.yml

we do not need the nightly build to run on `push`

Author: chrjohn

.github/workflows/nightly-build.yml

@@ -5,9 +5,6 @@ permissions:
 
 on:
   workflow_dispatch:
-  push:
-    branches:
-      - master
   schedule:
     - cron: '0 1 * * *'