Warning when add custom Mix task in project

[7sDream]

1. create a project with mix
2. create folder lib/mix/tasks
3. add start.ex in lib/mix/tasks with content:

defmodule Mix.Tasks.Start do
  use Mix.Task

  def run(_), do: "Hello World" |> IO.puts
end

Elixir Linter will show a warning on line 1: [ElixirLS Dialyzer] Callback info about the 'Elixir.Mix.Task' behaviour is not available

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Append: After I follow those steps on stackoverflow, run mix dialyzer in shell don't show warnings anymore, but VS Code keep showing.

[7sDream]

Sorry, the warning is issued by another extension.