Deploy to staging on merge to main branch (#16)

Author: arinchoi03

.github/workflows/deploy-to-staging.yml

@@ -1,9 +1,7 @@
 name: Deploy to AWS Staging
 
 on:
-  workflow_run:
-    workflows: [ "Run tests" ]
-    types: [ completed ]
+  push:
     branches: [ main ]
   workflow_dispatch:
     inputs: { }