Testsuite: T6494: add new make target "test-interfaces" (backport #796)

[mergify]

Change Summary

We can not run the interface related tests, and non interface related testcases in parallel to speedup the entire build process.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://vyos.dev/T6494

Related PR(s)

• GitHub: T6494: add parallel step to run interface based smoketests vyos-1x#4133
• T6494: add parallel step to run interface based smoketests vyos-nightly-build#7

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

---

This is an automatic backport of pull request #796 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 57d5afe has failed:

On branch mergify/bp/sagitta/pr-796
Your branch is up to date with 'origin/sagitta'.

You are currently cherry-picking commit 57d5afe0.
  (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:   Makefile
	both modified:   scripts/check-qemu-install

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

[github-actions]

👍
No issues in PR Title / Commit Title

[github-actions]

Conflicts have been resolved. A maintainer will review the pull request shortly.

[c-po]

Missing base PR for this backport. Closing as not that relevant