Prevent debugger from printing to STDOUT (#1968)

Author: vinistock

exe/ruby-lsp

@@ -75,14 +75,18 @@ require "ruby_lsp/internal"
 
 if options[:debug]
   if ["x64-mingw-ucrt", "x64-mingw32"].include?(RUBY_PLATFORM)
-    puts "Debugging is not supported on Windows"
+    $stderr.puts "Debugging is not supported on Windows"
     exit 1
   end
 
   begin
+    original_stdout = $stdout
+    $stdout = $stderr
     require "debug/open_nonstop"
   rescue LoadError
-    warn("You need to install the debug gem to use the --debug flag")
+    $stderr.puts("You need to install the debug gem to use the --debug flag")
+  ensure
+    $stdout = original_stdout
   end
 end