Enable Azure Linux 4.0 VM Tests

[vinceaperri]

This PR adds the following tests for Azure Linux 4.0:

• test_min_change_efi_azl4_qcow_output
• test_min_change_legacy_azl4_qcow_output
• test_min_change_efi_azl4_iso_bootstrap_output (skipped until ISO output is supported)
• test_min_change_efi_azl4_iso_full_os_output (skipped until ISO output is supported)
• test_min_change_legacy_azl4_iso_output (skipped until ISO output is supported)

Follow-up tasks:

• When another kernel release is available for Azure Linux 4.0 Alpha 2: change kernel-6.18.5-1.8.azl4~20260420 to a different release in os-vm-config-*-azl4.yaml, iso-full-os-vm-azl4.yaml, iso-bootstrap-vm-azl4.yaml

[Copilot]

Pull request overview

Adds Azure Linux 4.0 coverage to the imagecustomizer VM test suite by introducing AZL4-specific test configs, wiring new fixtures/options, and updating CI to fetch AZL4 base images.

Changes:

• Added AZL4 testdata configs for qcow2 + (currently skipped) ISO scenarios.
• Extended test_min_change.py to run AZL4 EFI + legacy qcow2 tests and updated AZL3 tests to use arch/release-specific configs.
• Updated vmtests harness (pytest options/fixtures, Makefile, and GitHub Actions workflow) to pass/download AZL4 input images.

Reviewed changes

Copilot reviewed 10 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
toolkit/tools/pkg/imagecustomizerlib/testdata/os-vm-config-arm64-azl4.yaml	New AZL4 arm64 OS VM config (kernel/package set).
toolkit/tools/pkg/imagecustomizerlib/testdata/os-vm-config-arm64-azl3.yaml	New AZL3 arm64 OS VM config used by vmtests.
toolkit/tools/pkg/imagecustomizerlib/testdata/os-vm-config-amd64-azl4.yaml	New AZL4 amd64 OS VM config (kernel/package set).
toolkit/tools/pkg/imagecustomizerlib/testdata/os-vm-config-amd64-azl3.yaml	New AZL3 amd64 OS VM config used by vmtests.
toolkit/tools/pkg/imagecustomizerlib/testdata/iso-full-os-vm-azl4.yaml	New AZL4 full-OS ISO config (tests currently skipped).
toolkit/tools/pkg/imagecustomizerlib/testdata/iso-full-os-vm-azl3.yaml	Minor formatting alignment with other ISO configs.
toolkit/tools/pkg/imagecustomizerlib/testdata/iso-bootstrap-vm-azl4.yaml	New AZL4 bootstrap ISO config (tests currently skipped).
toolkit/tools/pkg/imagecustomizerlib/testdata/iso-bootstrap-vm-azl3.yaml	Minor formatting alignment with other ISO configs.
test/vmtests/vmtests/imagecustomizer/test_min_change.py	Adds AZL4 qcow2 tests, updates config selection, and extends /etc/os-release checks.
test/vmtests/vmtests/imagecustomizer/conftest.py	Adds AZL4 CLI options + fixtures for core EFI/legacy images.
test/vmtests/Makefile	Passes AZL4 image paths into pytest invocation.
.github/workflows/tests-vmtests.yml	Downloads AZL4 base images and plumbs paths into vmtests CI run.

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[liulanze]

LGTM. And the comment from AI looks reasonable to me.