Compare a table message's filtered html as markup

The filters can write the same table with or without newlines between
its rows depending on which tests ran first in the process, so the exact
string comparison failed under some seeds. main compares it as markup.

test/helpers/content_filters_test.rb

@@ -172,7 +172,7 @@ class ContentFiltersTest < ActionView::TestCase
 
     filtered = ContentFilters::TextMessagePresentationFilters.apply(message.body.body).to_html
 
-    assert_equal body, filtered
+    assert_dom_equal body, filtered
     assert_match %r{<table>.*<th><p>Name</p></th>.*<td><p>Jason</p></td>}m, message_presentation(message)
   end