Add tests for system actor protection and hiding

Index: system actor not in list, destroy returns Ash.Error.Invalid. Show/Form:
redirect to /users when viewing or editing system actor user.

test/mv_web/live/user_live/show_test.exs

@@ -154,4 +154,14 @@ defmodule MvWeb.UserLive.ShowTest do
       assert html =~ gettext("Show User") || html =~ to_string(user.email)
     end
   end
+
+  describe "system actor user" do
+    test "redirects to user list when viewing system actor user", %{conn: conn} do
+      system_actor = Mv.Helpers.SystemActor.get_system_actor()
+      conn = conn_with_oidc_user(conn)
+
+      assert {:error, {:live_redirect, %{to: "/users"}}} =
+               live(conn, ~p"/users/#{system_actor.id}")
+    end
+  end
 end