Fix extra blank line when no error_highlight

A new condition was recently [added][1] to exclude error_highlight from
the Gemfile when the Ruby version is 3.2 or greater. However, this
change leads to an extra blank line after `gem "spring"` on Ruby 3.2+.
This could also happen to new apps generated on Rubies < 3.1, but my
guess is that is less common.

This commit fixes the issue by moving the extra blank line into the
condition.

[1]: d7b3951

Author: skipkayhil

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

@@ -50,8 +50,8 @@ group :development do
 <%- end -%>
   # Speed up commands on slow machines / big apps [https://github.com/rails/spring]
   # gem "spring"
-
 <%- if RUBY_VERSION >= "3.1" && RUBY_VERSION < "3.2" -%>
+
   gem "error_highlight", ">= 0.4.0", platforms: [:ruby]
 <%- end -%>
 end