[confcom] Fix test which pulls image and tests layers

[DomAyre]

Why

There is a test for the confcom extension which pulls a docker image by tag, and then asserts layer hashes match, this breaks regularly because the image changes between invocations.

This PR fixes that test

How

• Update the expected layer hashes to match what we get now
• Update the image reference and the code which pulls the image to ask for a specific image sha, this should prevent the layer hashes changing under us again

---

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Related command

az confcom

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[azure-client-tools-bot-prd]

Validation for Breaking Change Starting...

Thanks for your contribution!

[azure-client-tools-bot-prd]

Hi @DomAyre,
Please write the description of changes which can be perceived by customers into HISTORY.rst.
If you want to release a new extension version, please update the version in setup.py as well.

[Copilot]

Pull Request Overview

This PR fixes a flaky test in the confcom extension that was failing due to Docker image layer hashes changing when the image was updated. The fix ensures test stability by pinning to a specific image SHA instead of relying on a mutable tag.

• Updated the container image reference to use a specific SHA256 digest instead of a tag
• Modified the image pulling logic to use the full container image reference
• Updated the expected layer hashes to match the pinned image

[yonzhan]

Thank you for your contribution! We will review the pull request and get back to you soon.

[github-actions]

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[github-actions]

• For more info about extension versioning, please refer to Extension version schema

[DomAyre]

Since this is a test fix, no changes in HISTORY.rst or bump to version is needed