doc/go1.23: document "net/http".Request.CookiesNamed method

CL 511516 added the method but didn't include a release note for it
because it was authored and tested before the new release note flow.

For #61472.

Change-Id: I38f73e97093a2badaea658ed430e174b73e35b3a
Reviewed-on: https://go-review.googlesource.com/c/go/+/571278
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Emmanuel Odeke <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Commit-Queue: Michael Knyszek <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>

Author: dmitshur

doc/next/6-stdlib/99-minor/net/http/61472.md

@@ -0,0 +1 @@
+The new [Request.CookiesNamed] method retrieves all cookies that match the given name.