Fix vendor exclusion pattern to match vendor at any depth

Change vendor/**/* to **/vendor/**/* to properly exclude vendor directories
in subdirectories like react_on_rails/vendor/bundle/ and
react_on_rails_pro/vendor/bundle/ where CI installs gems.

Co-authored-by: Ihab Adham <ihabadham@users.noreply.github.com>

Author: github-actions[bot]

.rubocop.yml

@@ -27,7 +27,7 @@ AllCops:
     - 'node_modules/**/*'
     - 'spec/fixtures/**/*'
     - 'spec/react_on_rails/dummy-for-generators/**/*'
-    - 'vendor/**/*'
+    - '**/vendor/**/*'
 
 Naming/FileName:
   Exclude: