Only run on schedule, not merges (#3260)

#### Does this PR need a docs update or release note?

- [ ] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [x] ⛔ No

#### Type of change

- [ ] 🌻 Feature
- [x] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Supportability/Tests
- [x] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

.github/workflows/nightly_test.yml

@@ -6,10 +6,6 @@ on:
     # Run every day at 0 minutes and 0 hours (midnight GMT)
     - cron: "0 0 * * *"
 
-  push:
-    branches: [main]
-    tags: ["v*.*.*"]
-
 permissions:
   # required to retrieve AWS credentials
   id-token: write