internal/history: document Go 1.21.2 and 1.20.9 releases

Change-Id: Ida8e46ae0c8cd6241a96eac5565310b8b767d307
Reviewed-on: https://go-review.googlesource.com/c/website/+/533255
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>

internal/history/release.go

@@ -14,6 +14,22 @@ import "html/template"
 //
 // The table is sorted by date, breaking ties with newer versions first.
 var Releases = []*Release{
+	{
+		Date: Date{2023, 10, 5}, Version: Version{1, 21, 2},
+		Security: &FixSummary{Quantifier: "one", Packages: []string{"cmd/go"}},
+		Bug: &FixSummary{
+			Components: []template.HTML{"the compiler", "the <code>go</code> command", "the linker", "the runtime"},
+			Packages:   []string{"runtime/metrics"},
+		},
+	},
+	{
+		Date: Date{2023, 10, 5}, Version: Version{1, 20, 9},
+		Security: &FixSummary{Quantifier: "one", Packages: []string{"cmd/go"}},
+		Bug: &FixSummary{
+			Components: []template.HTML{"the <code>go</code> command", "the linker"},
+			Packages:   []string{},
+		},
+	},
 	{
 		Date: Date{2023, 9, 6}, Version: Version{1, 21, 1},
 		Security: &FixSummary{Quantifier: "four", Packages: []string{"cmd/go", "crypto/tls", "html/template"}},