Refactor file path in actions-validate.yml and add output for changed files

.github/actions/setup-env/action.yml

@@ -1,5 +1,9 @@
 name: Setup Environment
 description: Prepare the environment for A13labs CI/CD pipelines
+outputs:
+  changed_files:
+    description: The list of changed files in the current pull request
+    value: ${{ steps.get_changed_files.outputs.CHANGED_FILES }}
 
 runs:
   using: "composite"