update ci.yml to act on renamed main branch only

Author: DiegoPino

.github/workflows/ci.yml

@@ -1,9 +1,9 @@
 name: CI
 on:
   push:
-    branches: [ master ]
+    branches: [ main ]
   pull_request:
-    branches: [ master ]
+    branches: [ main ]
 jobs:
   build:
     runs-on: ${{ matrix.operating-system }}