fix tests

apps/block_scout_web/config/config.exs

@@ -42,7 +42,7 @@ config :block_scout_web, BlockScoutWeb.Endpoint,
     path: System.get_env("NETWORK_PATH") || "/"
   ],
   render_errors: [view: BlockScoutWeb.ErrorView, accepts: ~w(html json)],
-  pubsub: [name: BlockScoutWeb.PubSub, adapter: Phoenix.PubSub.PG2]
+  pubsub: [name: BlockScoutWeb.PubSub]
 
 config :block_scout_web, BlockScoutWeb.Tracer,
   service: :block_scout_web,

apps/block_scout_web/lib/block_scout_web/application.ex

@@ -18,6 +18,7 @@ defmodule BlockScoutWeb.Application do
     # Define workers and child supervisors to be supervised
     children = [
       # Start the endpoint when the application starts
+      {Phoenix.PubSub.PG2, name: BlockScoutWeb.PubSub, fastlane: Phoenix.Channel.Server},
       supervisor(Endpoint, []),
       supervisor(Absinthe.Subscription, [Endpoint]),
       {RealtimeEventHandler, name: RealtimeEventHandler},