Add missing expectation to annotations test

This expectations in this test were true both before and after clicking
on the `.icon-expand` link, so it was possible that the test finished
before the request generated by that click did.

So we're adding an extra expectation to make sure we're testing what we
want to test: the content of the page after the request has finished.

spec/system/comments/legislation_annotations_spec.rb

@@ -39,9 +39,10 @@ describe "Commenting legislation annotations" do
         find(".icon-expand").click
       end
 
-      expect(page).to have_css(".comment", count: 2)
-      expect(page).to have_content("my annotation")
-      expect(page).to have_content("my other annotation")
+      expect(page).to have_content "Comments about"
+      expect(page).to have_css ".comment", count: 2
+      expect(page).to have_content "my annotation"
+      expect(page).to have_content "my other annotation"
     end
 
     scenario "Reply on a single annotation thread and display it in the merged annotation thread" do