Temp fixup for elixir-mint/hpax#27

Author: mtrudel

lib/bandit/http2/connection.ex

@@ -300,7 +300,8 @@ defmodule Bandit.HTTP2.Connection do
   # Header list size per RFC9113§6.5.2
   defp header_list_size(headers) do
     Enum.reduce(headers, 0, fn {name, value}, acc ->
-      acc + byte_size(name) + byte_size(value) + 32
+      # drop the `|| ""` once we depend on a hpax release with elixir-mint/hpax#27,
+      acc + byte_size(name) + byte_size(value || "") + 32
     end)
   end