We changed the way we track Go threads in syscalls/cgo calls, which allowed us to remove one atomic store and one atomic compare-and-swap from the cgo call path. https://go.dev/cl/646198 and https://go.dev/cl/708596 are the relevant changes.

(It's basically an easter egg, but if you look at the source of the release notes, you will see that most entries in the release notes have an HTML comment referencing the Go CL or issue that the entry refers to.)