Fix Performance/StringIdentifierArgument violation in site.rb and allow activesupport 6 for windows tests (#9512)

Merge pull request 9512

Gemfile

@@ -15,7 +15,7 @@ end
 #
 
 group :test do
-  gem "activesupport", "~> 7.0.0"
+  gem "activesupport", "< 7.1.0"
   gem "cucumber", RUBY_VERSION >= "2.5" ? "~> 5.1.2" : "~> 4.1"
   gem "httpclient"
   gem "jekyll_test_plugin"

lib/jekyll/site.rb

@@ -49,7 +49,7 @@ module Jekyll
 
       %w(safe lsi highlighter baseurl exclude include future unpublished
          show_drafts limit_posts keep_files).each do |opt|
-        send("#{opt}=", config[opt])
+        send(:"#{opt}=", config[opt])
       end
 
       # keep using `gems` to avoid breaking change