Add pokémon clauses for unknown info messages

This is meant to protect against CaughtUp/FellBehind notifications
introduced in
<EventStore/EventStore@80d6546#diff-3f4777412535c46201e919412884d13ba6036db276eefe40ba84b8089b0c58f4>
but it should be safe to ignore any other unknown info notifications as
well.

lib/volley/in_order_subscription.ex

@@ -458,6 +458,10 @@ defmodule Volley.InOrderSubscription do
     {:stop, reason, state}
   end
 
+  def handle_info(_, state) do
+    {:noreply, [], state}
+  end
+
   # coveralls-ignore-stop
 
   defp read_stream(state, demand) do

lib/volley/persistent_subscription.ex

@@ -163,6 +163,10 @@ defmodule Volley.PersistentSubscription do
     {:noreply, [map_event(event, state)], state}
   end
 
+  def handle_info(_, state) do
+    {:noreply, [], state}
+  end
+
   @impl GenStage
   def handle_demand(_demand, state) do
     {:noreply, [], state}