Fix spec for which_children, closes #11005

Author: josevalim

lib/elixir/lib/dynamic_supervisor.ex

@@ -419,7 +419,7 @@ defmodule DynamicSupervisor do
   @doc since: "1.6.0"
   @spec which_children(Supervisor.supervisor()) :: [
           # module() | :dynamic here because :supervisor.modules() is not exported
-          {:undefined, pid | :restarting, :worker | :supervisor, module() | :dynamic}
+          {:undefined, pid | :restarting, :worker | :supervisor, [module()] | :dynamic}
         ]
   def which_children(supervisor) do
     call(supervisor, :which_children)

lib/elixir/lib/supervisor.ex

@@ -930,7 +930,7 @@ defmodule Supervisor do
   """
   @spec which_children(supervisor) :: [
           # inlining module() | :dynamic here because :supervisor.modules() is not exported
-          {term() | :undefined, child | :restarting, :worker | :supervisor, module() | :dynamic}
+          {term() | :undefined, child | :restarting, :worker | :supervisor, [module()] | :dynamic}
         ]
   def which_children(supervisor) do
     call(supervisor, :which_children)