chore: add gitHub actions workflow to validate pr's

Author: ashutosh-7503

.github/workflows/validate.yml

@@ -0,0 +1,16 @@
+name: Validate PR
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+jobs:
+  check-files:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Check for unwanted files
+        run: |
+          git diff --name-only origin/main | grep -E '(^\.dart_tool/|pubspec.lock)' && \
+          echo "❌ Unwanted file changes detected. Please remove pubspec.lock or .dart_tool changes." && exit 1 || \
+          echo "✅ No unwanted file changes."