Update tests

lib/nulla_web/controllers/actor_controller.ex

@@ -6,7 +6,7 @@ defmodule NullaWeb.ActorController do
   alias Nulla.Models.InstanceSettings
 
   def show(conn, %{"username" => username}) do
-    accept = List.first(get_req_header(conn, "accept"))
+    format = Phoenix.Controller.get_format(conn)
     instance_settings = InstanceSettings.get_instance_settings!()
     domain = instance_settings.domain
 
@@ -17,7 +17,7 @@ defmodule NullaWeb.ActorController do
         |> json(%{error: "Not Found"})
 
       %Actor{} = actor ->
-        if accept in ["application/activity+json"] do
+        if format == "activity+json" do
           conn
           |> put_resp_content_type("application/activity+json")
           |> send_resp(200, Jason.encode!(ActivityPub.actor(actor)))