internal/history: document future Go 1.21.3 and 1.20.10 releases

Change-Id: I88ba2892c8a0e953f0179dbd59eae9f43d1ecbce
Reviewed-on: https://go-review.googlesource.com/c/website/+/533955
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

internal/history/release.go

@@ -14,6 +14,16 @@ import "html/template"
 //
 // The table is sorted by date, breaking ties with newer versions first.
 var Releases = []*Release{
+	{
+		Date: Date{2023, 10, 10}, Version: Version{1, 21, 3},
+		Future:   true,
+		Security: &FixSummary{Quantifier: "a", Components: []template.HTML{"the standard library"}},
+	},
+	{
+		Date: Date{2023, 10, 10}, Version: Version{1, 20, 10},
+		Future:   true,
+		Security: &FixSummary{Quantifier: "a", Components: []template.HTML{"the standard library"}},
+	},
 	{
 		Date: Date{2023, 10, 5}, Version: Version{1, 21, 2},
 		Security: &FixSummary{Quantifier: "one", Packages: []string{"cmd/go"}},