_content/doc/go1.26: mention planned removal of nosizespecializedmalloc GOEXPERIMENT

Change-Id: I88a1b7f2effeb367818cff8c3a4eec1d5b33f47f
Reviewed-on: https://go-review.googlesource.com/c/website/+/733261
Reviewed-by: Michael Matloob <matloob@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Matloob <matloob@golang.org>

_content/doc/go1.26.md

diff --git a/_content/doc/go1.26.md b/_content/doc/go1.26.md
index 5d575bd..c75e6c4 100644
--- a/_content/doc/go1.26.md
+++ b/_content/doc/go1.26.md
@@ -122,6 +122,7 @@
 Please [file an issue](/issue/new) if you notice any regressions.
 You may set `GOEXPERIMENT=nosizespecializedmalloc` at build time to disable
 it.
+This opt-out setting is expected to be removed in Go 1.27.
 
 ### Goroutine leak profiles {#goroutineleak-profiles}