Fix operation passed to assert_no_null_byte (#6397)

Author: GriffinMB

lib/elixir/lib/file.ex

@@ -955,7 +955,7 @@ defmodule File do
   def rm_rf(path) do
     path
     |> IO.chardata_to_string()
-    |> assert_no_null_byte!("File.cp_r/3")
+    |> assert_no_null_byte!("File.rm_rf/1")
     |> do_rm_rf({:ok, []})
   end