doc: move ERR_WORKER_UNSPPORTED_EXTENSION to legacy

PR-URL: #39788
Fixes: #39124
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Bradley Farias <bradley.meck@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

Author: Ayase-252

doc/api/errors.md

@@ -2828,6 +2828,16 @@ Used when a given value is out of the accepted range.
 
 The module must be successfully linked before instantiation.
 
+<a id="ERR_WORKER_UNSUPPORTED_EXTENSION"></a>
+### `ERR_WORKER_UNSUPPORTED_EXTENSION`
+<!-- YAML
+added: v11.0.0
+removed: REPLACEME
+-->
+
+The pathname used for the main script of a worker has an
+unknown file extension.
+
 <a id="ERR_ZLIB_BINDING_CLOSED"></a>
 ### `ERR_ZLIB_BINDING_CLOSED`
 <!-- YAML