Make "tags" arch-specific again

This fixes edge case bugs where tags which share a sourceId but across disparate architectures will be grouped.

This can be seen concretely in https://oci.dag.dev/?image=infosiftr/moby:s390x@sha256:9a423230716c0f934e2fffa46585df1b2babc96ea0a1dd01bbd6ce29c6233aea (where `infosiftr/moby:s390x` should be _just_ the s390x build, but instead gets _all_ the architecture builds which share that same sourceId).

Author: tianon

.test/builds.json

@@ -1,6 +1,6 @@
 include "deploy";
 
 # every single ref both "library/" and arch-specific we should push to
-tagged_manifests(true; .source.tags, .source.arches[.build.arch].archTags)
+tagged_manifests(true; .source.arches[.build.arch].tags, .source.arches[.build.arch].archTags)
 # ... converted into a list of canonical inputs for "cmd/deploy"
 | deploy_objects

.test/deploy-all/out.json

@@ -10,6 +10,6 @@ include "meta";
 	| commands
 	| to_entries
 	| map("# <\(.key)>\n\(.value)\n# </\(.key)>")
-	| "# \($b.source.tags[0]) [\($b.build.arch)]\n" + join("\n")
+	| "# \($b.source.arches[$b.build.arch].tags[0]) [\($b.build.arch)]\n" + join("\n")
 )
 | join("\n\n")