Investigate feed-related intermittent test failures

   1) test gets a feed (RSS) (Pleroma.Web.Feed.TagControllerTest)
     test/web/feed/tag_controller_test.exs:84
     Assertion with == failed
     code:  assert xpath(xml, ~x"//channel/item/pubDate/text()"sl) == [FeedView.pub_date(activity1.data()["published"]), FeedView.pub_date(activity2.data()["published"])]
     left:  ["Wed, 15 Apr 20 10:18:22 +0000", "Wed, 15 Apr 20 10:18:22 +0000"]
     right: ["Wed, 15 Apr 20 10:18:21 +0000", "Wed, 15 Apr 20 10:18:22 +0000"]
     stacktrace:
       test/web/feed/tag_controller_test.exs:140: (test)

This seems like it might be an actual bug.