--all-platforms: make order deterministic

[vrothberg]

A combination of yet-to-be-resolved containers/common/issues/1295 and a non-deterministic processing of the platforms on the Buildah side caused heavy flakes, so make it deterministic.

[NO NEW TESTS NEEDED] - the expected absence of the flake will tell.

Fixes: #4520
Signed-off-by: Valentin Rothberg [email protected]

None

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[vrothberg]

@nalind @edsantiago PTAL

[nalind]

It's not the nondeterminism that's the bug here. While forcing the iteration order to match that of the base image's manifest list will have that effect with jobs == 1, I don't think it can guarantee stable ordering when jobs > 1.
The manifest list that lets us see the problem also lists its linux/arm/v6 image immediately before its linux/arm/v7 image, so I think for the jobs == 1 case that the test runs, it'll just start erroring out every time.