limit github actions to main branch

.github/workflows/notifications.yml

@@ -1,6 +1,8 @@
-name: regression check
+name: Send Notifications
 
-on: [push]
+on:
+  push:
+    branches: [ main ]
 
 jobs:
   send-notifications:

.github/workflows/testing.yml

@@ -1,6 +1,10 @@
 name: Build and Test
 
-on: [push, pull_request]
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
 
 jobs:
   regression-check: