Changelog (https://github.com/symfony/symfony/compare/v6.4.20...v6.4.21)

• bug #60288 [VarExporter] dump default value for property hooks if present (@xabbuh)
• bug #60268 [Contracts] Fix ServiceSubscriberTrait for nullable service (@StevenRenaux)
• bug #60256 [Mailer][Postmark] drop the Date header using the API transport (@xabbuh)
• bug #60258 [VarExporter] Fix: Use correct closure call for property-specific logic in $notByRef (@Hakayashii, @denjas)
• bug #60269 [Notifier] [Discord] Fix value limits (@norkunas)
• bug #60248 [Messenger] Revert " Add call to gc_collect_cycles() after each message is handled" (@jwage)
• bug #60236 [String] Support nexus -> nexuses pluralization (@KorvinSzanto)
• bug #60194 [Workflow] Fix dispatch of entered event when the subject is already in this marking (@lyrixx)
• bug #60172 [Cache] Fix invalidating on save failures with Array|ApcuAdapter (@nicolas-grekas)
• bug #60122 [Cache] ArrayAdapter serialization exception clean $expiries (@bastien-wink)
• bug #60167 [Cache] Fix proxying third party PSR-6 cache items (Dmitry Danilson)
• bug #60165 [HttpKernel] Do not ignore enum in controller arguments when it has an #[Autowire] attribute (@ruudk)
• bug #60168 [Console] Correctly convert SIGSYS to its name (@cs278)
• bug #60166 [Security] fix(security): fix OIDC user identifier (@vincentchalamon)
• bug #60124 [Validator] : fix url validation when punycode is on tld but not on domain (@joelwurtz)
• bug #60057 [Mailer] Fix Trying to access array offset on value of type null error by adding null checking (@khushaalan)
• bug #60094 [DoctrineBridge] Fix support for entities that leverage native lazy objects (@nicolas-grekas)
• bug #60094 [DoctrineBridge] Fix support for entities that leverage native lazy objects (@nicolas-grekas)

[PR] https://github.com/symfony/symfony/pull/60324