allow each image to have its own cache

[pdabelf5]

Proposed changes

Reading https://docs.docker.com/build/cache/backends/gha/#scope describes needing to change the scope when caching multiple docker builds to prevent the last image being cached as the only one in the cache.

Checklist

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• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork