doc/go1.21: add a release note for CL 463177
I'm not sure why the relnote tool did not fill in a TODO for that
change; one was requested in
http://go.dev/cl/c/go/+/463177/3#message-
87065dffb06e196fba9a325fefb32f16b41b6b15.
Updates #50807.
Updates #27225.
Change-Id: If6be8c126bcafb04ba92de88d2fc74a0557a07b8
Reviewed-on: https://go-review.googlesource.com/c/go/+/509098
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>