Use pre-imported container images in the tests to avoid hitting the API limit

[OneBlue]

Summary of the Pull Request

This change updates our test to use the pre-installed test images instead of pulling from the docker registry

PR Checklist

• Closes: Link to issue #xxx
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated if needed and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated if needed
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[Copilot]

Pull request overview

Updates WSLC tests to rely on pre-imported base images (instead of pulling from Docker Hub) to reduce registry/API-limit related failures in CI and local test runs.

Changes:

• Switch Dockerfiles used in WSLC build-related tests from alpine to debian:latest.
• Ensure the Debian test image is loaded for the WSLC E2E image build tests (and cleaned up afterward).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
test/windows/wslc/e2e/WSLCE2EImageBuildTests.cpp	Loads the pre-imported Debian base image for E2E image-build tests and updates test Dockerfiles to FROM debian:latest.
test/windows/WSLCTests.cpp	Updates multiple build-image API tests to use FROM debian:latest, aligning with images preloaded in test setup.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.