DEV: more resilient scroll to bottom spec (#21467)

The spec now checks we are in the state we expect to be before clicking bottom button. The bottom button could show while it's still loading and on slow systems cause failures.

plugins/chat/spec/system/navigating_to_message_spec.rb

@@ -62,7 +62,15 @@ RSpec.describe "Navigating to message", type: :system, js: true do
         chat_page.visit_channel(channel_1)
 
         click_link(link)
+
+        expect(page).to have_css(
+          ".chat-message-container.highlighted[data-id='#{first_message.id}']",
+        )
+
         click_button(class: "chat-scroll-to-bottom")
+
+        expect(page).to have_content(link)
+
         click_link(link)
 
         expect(page).to have_css(