ci: bump dead ubuntu 20.04

[Borda]

What does this PR do?

ubuntu 20.04 was removed from all runners so we need to bump to 22.04

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📚 Documentation preview 📚: https://pytorch-lightning--20719.org.readthedocs.build/en/20719/

[github-actions]

⚡ Required checks status: All passing 🟢

Groups summary

🟢 pytorch_lightning: Tests workflow

Check ID	Status
pl-cpu-guardian	success	✅

These checks are required after the changes to .github/workflows/ci-tests-pytorch.yml.

🟢 fabric: Docs

Check ID	Status
docs-make (fabric, doctest)	success	✅
docs-make (fabric, html)	success	✅

These checks are required after the changes to .github/workflows/docs-build.yml.

🟢 pytorch_lightning: Docs

Check ID	Status
docs-make (pytorch, doctest)	success	✅
docs-make (pytorch, html)	success	✅

These checks are required after the changes to .github/workflows/docs-build.yml.

🟢 lightning_fabric: CPU workflow

Check ID	Status
fabric-cpu-guardian	success	✅

These checks are required after the changes to .github/workflows/ci-tests-fabric.yml.

🟢 mypy

Check ID	Status
mypy	success	✅

These checks are required after the changes to .github/workflows/code-checks.yml.

---

Thank you for your contribution! 💜

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86%. Comparing base (03635d2) to head (8b4bbc7).
Report is 137 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #20719    +/-   ##
========================================
- Coverage      87%      86%    -1%     
========================================
  Files         268      268            
  Lines       23449    23449            
========================================
- Hits        20389    20253   -136     
- Misses       3060     3196   +136