Enable uvm kernel 6.1 tests

[Manciukic]

Changes

Enable microvm kernel 6.1 tests in preparation of release #4737.

This only applies to tests that use the fixture uvm_plain_any or derivatives. Tests using uvm_plain will continue using only 5.10. I did some tests with 6.1 kernel as default and uncovered some testing issues (not functional nor performance). I will push separate PRs to fix those.
Also, I didn't check the performance results yet, just that they passed.

Reason

We are phasing out support for 4.14, so we're adding the next supported LTS.

Questions

• Do we need to update any docs?

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the Apache 2.0 license. For more information on following Developer
Certificate of Origin and signing off your commits, please check
CONTRIBUTING.md.

PR Checklist

• If a specific issue led to this PR, this PR closes the issue.
• The description of changes is clear and encompassing.
• Any required documentation changes (code and docs) are included in this
  PR.
• API changes follow the Runbook for Firecracker API changes.
• User-facing changes are mentioned in CHANGELOG.md.
• All added/changed functionality is tested.
• New TODOs link to an issue.
• Commits meet
  contribution quality standards.

---

• This functionality cannot be added in rust-vmm.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.37%. Comparing base (a364da8) to head (d413f11).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4732   +/-   ##
=======================================
  Coverage   84.37%   84.37%           
=======================================
  Files         249      249           
  Lines       27433    27433           
=======================================
  Hits        23147    23147           
  Misses       4286     4286           

Flag	Coverage Δ
5.10-c5n.metal	84.60% <ø> (ø)
5.10-m5n.metal	84.58% <ø> (-0.01%)	⬇️
5.10-m6a.metal	83.87% <ø> (-0.01%)	⬇️
5.10-m6g.metal	80.90% <ø> (-0.01%)	⬇️
5.10-m6i.metal	84.58% <ø> (-0.01%)	⬇️
5.10-m7g.metal	80.91% <ø> (ø)
6.1-c5n.metal	84.60% <ø> (ø)
6.1-m5n.metal	84.58% <ø> (-0.01%)	⬇️
6.1-m6a.metal	83.88% <ø> (ø)
6.1-m6g.metal	80.91% <ø> (ø)
6.1-m6i.metal	84.58% <ø> (ø)
6.1-m7g.metal	80.90% <ø> (-0.01%)	⬇️

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