[8.18](backport #5123) bk: use ubuntu 22.04

[mergify]

What is the problem this PR solves?

// Please do not just reference an issue. Explain WHAT the problem this PR solves here.

How does this PR solve the problem?

22.04 is still under support https://en.wikipedia.org/wiki/Ubuntu_version_history

But 20.04 is under expanded security support

How to test this PR locally

Design Checklist

• I have ensured my design is stateless and will work when multiple fleet-server instances are behind a load balancer.
• I have or intend to scale test my changes, ensuring it will work reliably with 100K+ agents connected.
• I have included fail safe mechanisms to limit the load on fleet-server: rate limiting, circuit breakers, caching, load shedding, etc.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool

Related issues

---

This is an automatic backport of pull request #5123 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of fae7420 has failed:

On branch mergify/bp/8.18/pr-5123
Your branch is up to date with 'origin/8.18'.

You are currently cherry-picking commit fae7420.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .buildkite/pipeline.package.mbp.yml

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[prodsecmachine]

🎉 Snyk checks have passed. No issues have been found so far.

✅ security/snyk check is complete. No issues have been found. (View Details)

✅ license/snyk check is complete. No issues have been found. (View Details)

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarQube

[mergify]

This pull request has not been merged yet. Could you please review and merge it @v1v? 🙏