test: add note about unresolved spec issue

PR-URL: #50779
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

test/wpt/status/streams.json

@@ -11,6 +11,7 @@
   },
   "piping/general-addition.any.js": {
     "fail": {
+      "note": "Blocked on https://github.com/whatwg/streams/issues/1243",
       "expected": [
         "enqueue() must not synchronously call write algorithm"
       ]