update pr-url

Author: simon-id

doc/api/diagnostics_channel.md

@@ -266,7 +266,7 @@ added:
  - v14.17.0
 changes:
   - version: REPLACEME
-    pr-url: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/40433
     description: Added to channels without subscribers.
 -->