Don't require debug

This isn't needed for tests. But moreover, it causes an error on Ruby
3.0.

It opens with:

``ruby
if $SAFE > 0
  STDERR.print "-r debug.rb is not available in safe mode\n"
  exit 1
end
```

But `$SAFE` is not set, so we get `nil > 0`, and an error.

```
% ruby -rdebug -e 'puts "OK"'
/home/mike/.rubies/ruby-3.0.6/lib/ruby/3.0.0/debug.rb:9:in `<top (required)>': undefined method `>' for nil:NilClass (NoMethodError)
        from <internal:/home/mike/.rubies/ruby-3.0.6/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
        from <internal:/home/mike/.rubies/ruby-3.0.6/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
```

This is not an issue on Ruby 3.1.

features/support/rails_template

@@ -2,7 +2,8 @@ if Rails.gem_version < Gem::Version.new('6')
   gsub_file "Gemfile", /^gem 'sqlite3'$/, 'gem "sqlite3", "~> 1.3.6"'
 end
 
-gsub_file "Gemfile", /^ gem 'spring'$/, ' gem "spring", "!= 2.1.1"'
+gsub_file "Gemfile", /^  gem 'spring'$/, ' gem "spring", "!= 2.1.1"'
+gsub_file "Gemfile", /^  gem "debug".*/, ''
 
 if Rails.gem_version >= Gem::Version.new('7.1')
   append_to_file File.join("config", "application.rb"), <<~RUBY