Fix containers.conf download path

[alex1701c]

As part of https://github.com/containers/buildah/commit/36afa3530e5b2f290455968e89a5a4c82261773b, the stable part of the file path was removed.

Description

Related Issue(s)

Checklist

• [ ] This PR includes a documentation change
• [x] This PR does not need a documentation change

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• [ ] This PR includes test changes
• [x] This PR's changes are already tested

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• [x] This change is not user-facing
• [x] This change is a patch change
• [ ] This change is a minor change
• [ ] This change is a major (breaking) change

Changes made

Adjustment of URL

[alex1701c]

@nt-baker Could you review this?