Add inherit_mode merge for Exclude arrays in child configs

Without inherit_mode merge, child Exclude arrays replace the parent's
instead of merging with them. This was causing all root exclusions
(node_modules, tmp, coverage, etc.) to be lost in the child configs.

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

Author: github-actions[bot]

react_on_rails/.rubocop.yml

@@ -1,6 +1,11 @@
 # Inherits from root config
 inherit_from: ../.rubocop.yml
 
+# Merge Exclude arrays with parent instead of replacing them
+inherit_mode:
+  merge:
+    - Exclude
+
 AllCops:
   SuggestExtensions: false
 

react_on_rails_pro/.rubocop.yml

@@ -1,6 +1,11 @@
 # Inherits from root config
 inherit_from: ../.rubocop.yml
 
+# Merge Exclude arrays with parent instead of replacing them
+inherit_mode:
+  merge:
+    - Exclude
+
 AllCops:
   Exclude:
   <% `git status --ignored --porcelain`.lines.grep(/^!! /).each do |path| %>