BUG #16843: pg_upgrade from 12.5 to 13.1 with extension plperlu failed

The following bug has been logged on the website:

Bug reference:      16843
Logged by:          Thomas Steffen
Email address:      linreg@gmx.net
PostgreSQL version: 13.1
Operating system:   OpenSuse 15.2
Description:

Hello
In the upgrade process with pg_upgrade ( as user postgres) following error
occured:
Translated from German!
---- SNIPPET ----
pg_restore: create EXTENSION »plperlu«
pg_restore: create COMMENT »EXTENSION "plperlu"«
pg_restore: create PROCEDURAL LANGUAGE »plperlu«
pg_restore: in Phase PROCESSING TOC:
pg_restore: in Table of contents 2151; 2612 16427 PROCEDURAL LANGUAGE
plperlu postgres
pg_restore: Error: could not execute query: ERROR:  Language »plperlu« does
not exist
The statement was: CREATE OR REPLACE PROCEDURAL LANGUAGE "plperlu";

-- For binary upgrade, handle extension membership the hard way
ALTER EXTENSION "plperlu" ADD LANGUAGE "plperlu";

----- SNIPPET END -----

The last command can not be executed succesfully. ==> ALTER EXTENSION
"plperlu" ADD LANGUAGE "plperlu";
possible cause: 
This command "CREATE OR REPLACE PROCEDURAL LANGUAGE "plperlu";" 
does not create a LANGUAGE object. It creates only the extension object
plperlu!
This means the language cannot be added to this extension.

i think the workaround with 
> CREATE OR REPLACE PROCEDURAL LANGUAGE "plperlu";
> ALTER EXTENSION "plperlu" ADD LANGUAGE "plperlu"; 
for 
> CREATE EXTENSION "plperlu";
is not necessary.

best regards