livecheck: fix TTY output for progress bar

Library/Homebrew/livecheck/livecheck.rb

@@ -75,7 +75,10 @@ module Homebrew
           formulae_to_check.length
         end
 
-        $stderr.puts Formatter.headline("Running checks", color: :blue)
+        Tty.with($stderr) do |stderr|
+          stderr.puts Formatter.headline("Running checks", color: :blue)
+        end
+
         progress = ProgressBar.create(
           total:          total_formulae,
           progress_mark:  "#",
@@ -182,7 +185,9 @@ module Homebrew
 
       if progress
         progress.finish
-        $stderr.print "#{Tty.up}#{Tty.erase_line}" * 2
+        Tty.with($stderr) do |stderr|
+          stderr.print "#{Tty.up}#{Tty.erase_line}" * 2
+        end
       end
 
       puts JSON.generate(formulae_checked.compact)

Library/Homebrew/utils/tty.rb

@@ -88,7 +88,7 @@ module Tty
 
   SPECIAL_CODES.each do |name, code|
     define_singleton_method(name) do
-      if $stdout.tty?
+      if @stream.tty?
         "\033[#{code}"
       else
         ""