[Fix rubocop#636] Fix a false positive for Rails/ContentTag

Fixes rubocop#636.

This PR fixes a false positive for `Rails/ContentTag`
when using `tag` method in config/puma.rb.

changelog/fix_a_false_positive_for_rails_content_tag.md

@@ -0,0 +1 @@
+* [#636](https://github.com/rubocop/rubocop-rails/issues/636): Fix a false positive for `Rails/ContentTag` when using `tag` method in config/puma.rb. ([@koic][])

config/default.yml

@@ -195,9 +195,12 @@ Rails/ContentTag:
   Enabled: true
   VersionAdded: '2.6'
   VersionChanged: '2.12'
-  # This `Exclude` config prevents false positives for `tag` calls to `has_one: tag`. No helpers are used in normal models.
+  # This `Exclude` config prevents false positives for `tag` calls to `has_one: tag` and Puma configuration:
+  # https://puma.io/puma/Puma/DSL.html#tag-instance_method
+  # No helpers are used in normal models and configs.
   Exclude:
     - app/models/**/*.rb
+    - config/**/*.rb
 
 Rails/CreateTableWithTimestamps:
   Description: >-