chore: migrate away from deprecated JSON#fast_generate

Author: stainless-app[bot]

Rakefile

@@ -31,7 +31,7 @@ multitask(:test) do
     .map { "require_relative(#{_1.dump});" }
     .join
 
-  ruby(*%w[-e], rb, verbose: false) { fail unless _1 }
+  ruby(*%w[-w -e], rb, verbose: false) { fail unless _1 }
 end
 
 rubo_find = %w[find ./lib ./test ./rbi -type f -and ( -name *.rb -or -name *.rbi ) -print0]

lib/openai/internal/util.rb

@@ -493,7 +493,7 @@ class << self
             y << val.to_s
           else
             y << "Content-Type: application/json\r\n\r\n"
-            y << JSON.fast_generate(val)
+            y << JSON.generate(val)
           end
           y << "\r\n"
         end