Compare the image config when checking for a platform

The platform check used regctl manifest get --platform, which only
selects an entry inside a manifest list. Against a plain manifest it
succeeds whatever platform is asked for: an arm64-only tag answers yes
to linux/amd64, and to linux/ppc64le for that matter.

The tags this check exists for are plain manifests. skopeo copy without
--all writes a single manifest, so an amd64-only tag left behind by an
earlier run is exactly the case that slipped through, and the check went
on skipping the push it was added to allow.

regctl image config resolves the platform and reports the architecture
it actually found, so comparing that against the requested platform
distinguishes the two.

Signed-off-by: Abrar Shivani <ashivani@nvidia.com>

Author: abrarshivani

scripts/precompiled.sh

@@ -102,8 +102,9 @@ function imageExistsForAllTargetPlatforms(){
 	imageExists "$image" || return 1
 	local platform
 	for platform in $(targetPlatforms); do
-		# unlike --list, --platform fails when the manifest list carries no entry for that platform
-		regctl manifest get "$image" --platform "$platform" > /dev/null || return 1
+		# manifest get --platform only selects within a manifest list; against a
+		# single manifest it succeeds for any platform, so compare the config.
+		[ "$(regctl image config "$image" --platform "$platform" --format '{{.OS}}/{{.Architecture}}' 2>/dev/null)" = "$platform" ] || return 1
 	done
 	return 0
 }