Revert "Rails 8 will target Ruby 3.3+ only for new apps"

This reverts commit c78a6fa.

Main is still 7.2. Will reply when we release it.

Author: rafaelfranca

railties/lib/rails/generators/rails/app/templates/Gemfile.tt

@@ -51,6 +51,11 @@ end
 group :development do
   # Use console on exceptions pages [https://github.com/rails/web-console]
   gem "web-console"
+<%- if RUBY_VERSION < "3.2" -%>
+
+  # Highlight the fine-grained location where an error occurred [https://github.com/ruby/error_highlight]
+  gem "error_highlight", ">= 0.4.0", platforms: [:ruby]
+<%- end -%>
 end
 <%- end -%>