Fix CI: Tag image

Version Control Information

Source branch: fix/ci-tag-image
Target branch: devel

Commits:

* Fix CI: Use NixOS image for skopeo

* Fix CI: Export image tag before cleanup script

* Fix CI: Add tag-image stage before release stage

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Description

Feel free to add further information about your MR in this section

Closes: #

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Merge Prerequisites

• MR title (and description) are descriptive
• Code is readable and syntactically correct
• Code is understandable
• Documentation has been updated, if necessary
• Commit messages look good
• Release note file in RST format added in latest commit

As a developer: please do not tick these boxes yourself. As a reviewer: please get yourself a hot cold beverage.