chore: Update CI config to include nodejs v20

[rpl]

• fix next job (nodejs 20): updated testdouble + fix from Support develoment environment using Node.js 20 #2917 (comment) (matching new URL doesn't work like in nodejs < 20 and still needs that workaround)
• fix windows CI job: WebExtError: request to http://localhost:8989/fake/api/v5/addons/upload/ failed, reason: connect ECONNREFUSED ::1:8989 is the failure to fix
• fix or disable experimental job (nodejs 21): another flavor of the issue with mocking ESM module, the one that was hit by nodejs v20 was fixed by the last version of test double, this one unfortunately it isn't. Filed Re-introduce informative CI jobs covering nodejs experimental versions #3015 to track it as a follow up.

Fixes #2917

[rpl]

new attempt... 🤞

[willdurand]

r+wc, thanks

[rpl]

Thanks a lot to @yan12125 for reporting #2917 and invaluable help to investigate and fix it ❤️