Retry retried_entries for uncles

`Indexer.Block.Uncle.Fetcher.retry/1` when there are errors did not
actually retry the calculated `retried_errors` and instead only logged
them.  This didn't cause an unused variable warning because
`retried_errors` is used in the Logger metadata.  The `Task` for the
`run/2` callback did not error because `Logger.error` returns `:ok`.

To fix this problem, `{:retry, retried_errors}` need to be returned
after the `Logger.error` call.

apps/indexer/lib/indexer/block/uncle/fetcher.ex

@@ -199,6 +199,8 @@ defmodule Indexer.Block.Uncle.Fetcher do
       end,
       error_count: Enum.count(retried_entries)
     )
+
+    {:retry, retried_entries}
   end
 
   defp errors_to_entries(errors) when is_list(errors) do