Fixes a Python out of memory error that sometimes is reported when a client gets disconnected, reconnects, and then calls `resubscribe_existing_topics`
What's Changed
* Fix out of memory issue when resubscribing by TwistedTwigleg in https://github.com/awslabs/aws-crt-python/pull/393
**Full Changelog**: https://github.com/awslabs/aws-crt-python/compare/v0.14.5...v0.14.6