Add missing require

`activesupport/test/logger_test.rb` requires `tmpdir`.

`activesupport/test/multibyte_test_helpers.rb` requires
`filutils`, `open-uri`, and `tmpdir`.

activesupport/test/logger_test.rb

@@ -5,6 +5,7 @@
 require "stringio"
 require "fileutils"
 require "tempfile"
+require "tmpdir"
 require "concurrent/atomics"
 
 class LoggerTest < ActiveSupport::TestCase

activesupport/test/multibyte_test_helpers.rb

@@ -1,5 +1,9 @@
 # frozen_string_literal: true
 
+require "fileutils"
+require "open-uri"
+require "tmpdir"
+
 module MultibyteTestHelpers
   class Downloader
     def self.download(from, to)