doc/next: pre-announce dropping macOS 11 support

Go 1.24 is the last release that will run on macOS 11 Big Sur.
Go 1.25 will require macOS 12 Monterey or later.

For #69839.
For #23011.

Change-Id: Ic58beff0f7eb69f600add5c17cf6edd960d09980
Reviewed-on: https://go-review.googlesource.com/c/go/+/627616
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: David Chase <[email protected]>

Author: cherrymui

doc/next/7-ports.md

@@ -5,6 +5,12 @@
 As [announced](go1.23#linux) in the Go 1.23 release notes, Go 1.24 requires Linux
 kernel version 3.2 or later.
 
+### Darwin {#darwin}
+
+<!-- go.dev/issue/69839 -->
+Go 1.24 is the last release that will run on macOS 11 Big Sur.
+Go 1.25 will require macOS 12 Monterey or later.
+
 ### WebAssembly {#wasm}
 
 The support files for WebAssembly have been moved to `lib/wasm` from `misc/wasm`.