Update default ci trigger

Author: WeihanLi

.github/workflows/dotnetcore.yml

@@ -1,6 +1,14 @@
 name: default
 
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - "main"
+      - "dev"
+  pull_request:
+    # The branches below must be a subset of the branches above
+    branches:
+      - "dev"
 
 jobs:
   mac-build: