_content/doc: update go.dev/doc/toolchain's backport description

Match the behavior as implemented in CL 518675 and CL 518815,
and ready to be released in the next set of minor releases.

For golang/go#57001.

Change-Id: I4404530994e636173f636aefb83bd64e208eba3c
Reviewed-on: https://go-review.googlesource.com/c/website/+/519216
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

Author: dmitshur

_content/doc/toolchain.md

@@ -179,8 +179,8 @@ if builds succeeded the toolchain assumed everything worked,
 and if not it printed a note about the potential version mismatch.
 Go 1.21 changed the `go` line to be a mandatory requirement instead.
 This behavior is partly backported to earlier language versions:
-Go 1.19 releases starting at Go 1.19.11 and Go 1.20 releases starting at Go 1.20.6,
-refuse to load workspaces or modules declaring version Go 1.21 or later.
+Go 1.19 releases starting at Go 1.19.13 and Go 1.20 releases starting at Go 1.20.8,
+refuse to load workspaces or modules declaring version Go 1.22 or later.
 
 Before Go 1.21, toolchains did not require a module
 or workspace to have a `go` line greater than or equal to the