chore(ci): update pull_request target branch from master to main

Author: Venkata Subramani Renduchintala

.github/workflows/validate.yml

@@ -4,7 +4,7 @@ on:
   push:
     branches: ["**"]
   pull_request:
-    branches: [master]
+    branches: [main]
 
 jobs:
   validate: