updating release workflow

.github/workflows/release.yaml

@@ -1,6 +1,20 @@
 name: Build distribution
 
-on: [push, pull_request]
+on:
+  # GitHub has started calling new repo's first branch "main" https://github.com/github/renaming
+  # Existing codes likely still have "master" as the primary branch
+  # Both are tracked here to keep legacy and new codes working
+  push:
+    branches:
+      - "main"
+  pull_request:
+    branches:
+      - "main"
+  schedule:
+    # Nightly tests run on master by default:
+    #   Scheduled workflows run on the latest commit on the default or base branch.
+    #   (from https://help.github.com/en/actions/reference/events-that-trigger-workflows#scheduled-events-schedule)
+    - cron: "0 0 * * 1"   ## running every Monday at midnight
 
 jobs:
   test: