Fix type warning in test

Author: sabiwara

lib/elixir/test/elixir/version_test.exs

@@ -317,8 +317,10 @@ defmodule VersionTest do
     {:ok, req} = Version.parse_requirement("1.2.3")
     assert req == Version.compile_requirement(req)
 
+    string = Process.get(:unused, "~> 1.2.3")
+
     assert_raise(FunctionClauseError, fn ->
-      Version.compile_requirement("~> 1.2.3")
+      Version.compile_requirement(string)
     end)
   end