doc: add missing changes: entry for assert.throws

Refs: #20485

PR-URL: #20723
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>

Author: addaleax

doc/api/assert.md

@@ -1056,6 +1056,10 @@ instead of the `AssertionError`.
 <!-- YAML
 added: v0.1.21
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/20485
+    description: The `error` parameter can be an object containing regular
+                 expressions now.
   - version: v9.9.0
     pr-url: https://github.com/nodejs/node/pull/17584
     description: The `error` parameter can now be an object as well.