Requires selenium-webdriver 4.0.0

`selenium-webdriver` added support for Ruby 3.0, but there is only an RC version available right now.

Related to rails#43248

Author: ceritium

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

@@ -66,7 +66,7 @@ end
 group :test do
   # Use system testing [https://guides.rubyonrails.org/testing.html#system-testing]
   gem "capybara", ">= 3.26"
-  gem "selenium-webdriver"
+  gem "selenium-webdriver", ">= 4.0.0.rc1"
   gem "webdrivers"
 end
-<%- end -%>
+<%- end -%>