ci: build only on main, also nightly cronjob

.github/workflows/main.yml

@@ -1,4 +1,9 @@
-on: [push, workflow_dispatch]
+on:
+  push:
+    branches:
+      - main
+  schedule:
+    - cron: '0 0 * * *'
 
 jobs:
   build:
@@ -33,7 +38,7 @@ jobs:
       - name: upload
         uses: actions/upload-artifact@v3
         with:
-          name: build-${{matrix.os}}
+          name: zba-${{matrix.os}}
           path: zig-out/bin
   lint:
     runs-on: ubuntu-latest