CI: Save trees, only run toast updater on release event

[JacobCoffee]

The update-toast.yml workflow should only run when new litestar releases are cut. Research (and if possible implement) the usage of repository_dispatch or similar event kickoffs for workflows that will let us dynamically do this.

---

i wonder if we can use repository_dispatch to dynamically do this instead of killing trees

Originally posted by @JacobCoffee in #24 (comment)

[JacobCoffee]

https://github.com/peter-evans/create-pull-request/blob/main/docs/concepts-guidelines.md#creating-pull-requests-in-a-remote-repository