chore: Upgrade `jsdom` to v21 which still supports Node 14

[Fullchee]

What:

• Upgrade jsdom to v21 which still supports Node 14

Why:

• fixes https://github.com/testing-library/jest-dom/issues/570
• use the latest version of jsdom that supports Node 14

How:

Checklist:

• ~[ ] Documentation~
• ~[ ] Tests~
• ~[ ] Updated Type Definitions~
• [ ] Ready to be merged

[Fullchee]

@fpapado @gnapse

Do we want to release a new major release of jest-dom@7which still supports Node 14?

We're upgrading jsdom@16 to jsdom@21

• => 5 breaking changes which might unwittingly break things in this library too