test: verify Docker image comparison end to end

[Pyker]

Completed end-to-end verification; closed without merging. The released TechnicPack/docker-image-diff@v1 action ran without checkout, compared the real MariaDB digest pair, and updated comment #5735377509 in place after a second push. The update also inspected an added single-platform image. CI and both comment workflow runs passed. Temporary fixture branches were removed; the bot comment and workflow runs are retained as evidence.

[github-actions]

Docker image changes

Compared PR head 81c78ad85d1688338ad11448858dc134aa8ded9f against merge base 5b1872bd1f51758804459e7d52a8e7d2cad92d1f.

smoke/compose.yml — service:db

Before: mariadb:lts@sha256:adbf5727f3d6ffa0ea11109f948247d88d110edd3f43f8d4c134c0a09060c5f3
After: mariadb:lts@sha256:805c8e104bd563d5bfa24fadd3f31cd419ea859cb5277f32b5dbf2db714f9ed1

Platform	Version before	Version after	Image changed
linux/amd64	12.3.3-noble	12.3.3-noble	No
linux/arm64/v8	12.3.3-noble	12.3.3-noble	No
linux/ppc64le	12.3.3-noble	12.3.3-noble	No
linux/s390x	12.3.3-noble	12.3.3-noble	Yes

• linux/s390x — Base-image digest: sha256:4f37b40c0a33a7b548450f34300ad54254c14f7f896db27dd41e16f121b92d21 → sha256:d19ffc6e735c9a4c282af623ef469514567c89eda922a3e0706720eb03149de3

smoke/compose.yml — service:db-amd64

Before: Not present
After: mariadb@sha256:2f4f46f80e7251990bfdc601ae3f7f2964ddb4dc1868f7deca699fc1ece8c35e

Platform	Version before	Version after	Image changed
linux/amd64	Not present	12.3.3-noble	Added

Versions are publisher-provided OCI annotations or image labels, not runtime verification. Attestation manifests are excluded from platform comparisons.