Changelog (v6.4.20...v6.4.21)

• bug symfony/symfony#60172 [Cache] Fix invalidating on save failures with Array|ApcuAdapter (@nicolas-grekas)
• bug symfony/symfony#60122 [Cache] ArrayAdapter serialization exception clean $expiries (@bastien-wink)
• bug symfony/symfony#60167 [Cache] Fix proxying third party PSR-6 cache items (Dmitry Danilson)