Hi,
Thank you so much for this, I did some research and it turns out that our mirror repository follows the official Homebrew repo with an intended delay, so being that the latest 0.45.1 update is recent, we hope to bring this to our mirror repository soon in the coming updates. However, should you require this version now, there is a way to switch to the official Formula repo using a custom script that can be added as a step found in this article How to change brew core from mirror to official?. We hope that this helps in being able to access the latest version of swiftlint desired.
Thank you,
Lex