doc/next: add release note for new toolchain line behavior
The go command will now no longer update the toolchain line implicitly
to the local toolchain version when updating the go line. Document that
in a release note.
For #65847
Change-Id: I4e970d881a43c22292fe9fa65a9835d0214ef7bf
Reviewed-on: https://go-review.googlesource.com/c/go/+/657178 Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org> Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>