[Backport release-26.05] nixosTests/cosmic: move core logic into a dedicated script

[nixpkgs-ci]

Bot-based backport to release-26.05, triggered by a label in #519448.

Before merging, ensure that this backport is acceptable for the release.

Even as a non-committer, if you find that it is not acceptable, leave a comment.

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[thefossguy]

nixpkgs-review result

Generated using nixpkgs-review.

Command: nixpkgs-review pr 535620 --extra-nixpkgs-config '{ allowBroken = true; allowUnfree = true; }' --additional-package nixosTests.cosmic --additional-package nixosTests.cosmic-autologin --additional-package nixosTests.cosmic-noxwayland --additional-package nixosTests.cosmic-autologin-noxwayland
Commit: e28f220794c92f99421649b8549224349fbd7d57

---

aarch64-linux

✅ 4 tests built:

• nixosTests.cosmic
• nixosTests.cosmic-autologin
• nixosTests.cosmic-autologin-noxwayland
• nixosTests.cosmic-noxwayland

✅ 1 package built:

• empty-pdf

[thefossguy]

nixpkgs-review result

Generated using nixpkgs-review.

Command: nixpkgs-review pr 535620 --extra-nixpkgs-config '{ allowBroken = true; allowUnfree = true; }' --additional-package nixosTests.cosmic-autologin --additional-package nixosTests.cosmic-noxwayland --additional-package nixosTests.cosmic-autologin-noxwayland --additional-package nixosTests.cosmic
Commit: e28f220794c92f99421649b8549224349fbd7d57

---

x86_64-linux

✅ 4 tests built:

• nixosTests.cosmic
• nixosTests.cosmic-autologin
• nixosTests.cosmic-autologin-noxwayland
• nixosTests.cosmic-noxwayland

✅ 1 package built:

• empty-pdf

[thefossguy]

Backported NixOS VM tests are passing.

[thefossguy]

@NixOS/nixpkgs-merge-bot merge

[nixpkgs-ci]

@thefossguy wants to merge this PR.

Requirements to merge this PR with @NixOS/nixpkgs-merge-bot merge:

• ✅ PR targets a development branch.
• ❌ PR touches only files of packages in pkgs/by-name/.
• ✅ PR is at least one of:
  • ⬜ Approved by a committer.
  • ✅ Backported via label.
  • ⬜ Opened by a committer.
  • ⬜ Opened by @r-ryantm.
• ✅ PR is not a draft
• ✅ PR is not blocked by a "changes requested" review from a committer.
• ✅ thefossguy is a member of @NixOS/nixpkgs-maintainers.

❌ Pull Request could not be merged (#305350)