Prepare release v321 (heroku#1644)

Co-authored-by: heroku-linguist[bot] <136119646+heroku-linguist[bot]@users.noreply.github.com>

Author: heroku-linguist[bot]

CHANGELOG.md

@@ -3,6 +3,11 @@
 ## [Unreleased]
 
 
+## [v321] - 2025-09-16
+
+- Ruby 3.4.6 is now available
+
+
 ## [v320] - 2025-09-09
 
 - Set `export PUMA_PERSISTENT_TIMEOUT=95` to match recommended router 2.0 settings (https://github.com/heroku/heroku-buildpack-ruby/pull/1641)
@@ -1758,7 +1763,8 @@ Bugfixes:
 * Change gem detection to use lockfile parser
 * use `$RACK_ENV` when thin is detected for rack apps
 
-[unreleased]: https://github.com/heroku/heroku-buildpack-ruby/compare/v320...main
+[unreleased]: https://github.com/heroku/heroku-buildpack-ruby/compare/v321...main
+[v321]: https://github.com/heroku/heroku-buildpack-ruby/compare/v320...v321
 [v320]: https://github.com/heroku/heroku-buildpack-ruby/compare/v319...v320
 [v319]: https://github.com/heroku/heroku-buildpack-ruby/compare/v318...v319
 [v318]: https://github.com/heroku/heroku-buildpack-ruby/compare/v317...v318

lib/language_pack/version.rb

@@ -2,6 +2,6 @@
 
 module LanguagePack
   class LanguagePack::Base
-    BUILDPACK_VERSION = "v320"
+    BUILDPACK_VERSION = "v321"
   end
 end