Include hidden elements for turbo-cable-stream-source selector

Chrome considers these elements not visible (likely due to their 0px
size) so the assertion never matches. This changes the default visible
flag to include all elements.

Author: excid3

lib/turbo/system_test_helper.rb

@@ -80,6 +80,8 @@ def assert_no_turbo_cable_stream_source(...)
   end
 
   Capybara.add_selector :turbo_cable_stream_source do
+    visible :all
+
     xpath do |locator|
       xpath = XPath.descendant.where(XPath.local_name == "turbo-cable-stream-source")
       xpath.where(SignedStreamNameConditions.new(locator).reduce(:|))