Convert invites controller spec to system/request specs (#31755)

spec/support/matchers/private_cache_control.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+RSpec::Matchers.define :have_private_cache_control do
+  match do |page|
+    page.response_headers['Cache-Control'] == 'private, no-store'
+  end
+
+  failure_message do |page|
+    <<~ERROR
+      Expected page to have `Cache-Control` header with `private, no-store` but it has:
+        #{page.response_headers['Cache-Control']}
+    ERROR
+  end
+end