buildsys output includes misleading "Error" log when force-upstream or BUILDSYS_UPSTREAM_SOURCE_FALLBACK set

[ginglis13]

Description

If a package is built with force-upstream = true or BUILDSYS_UPSTREAM_SOURCE_FALLBACK=true, buildsys logs contain an error message that is a red herring for debugging build failures:

 cargo:rerun-if-changed=/local/home/dhwanise/bottlerocket-repos/codebuild_reproduce/bottlerocket-kernel-kit/build/external-kits/external-kit-metadata.json
  Error fetching from lookaside cache: Failed to fetch 'https://cache.bottlerocket.aws/aws-neuronx-dkms-2.19.64.0.noarch.rpm/f93aa097ea0515533817ce9737810cb8b025c35c3d4367c2e667292c0692d525ffbc9b7972fe957174e206a82e394cc7e076e5b399e1050f2c5f6ed129d4d739/aws-neuronx-dkms-2.19.64.0.noarch.rpm': 403 Forbidden
  Fetching "aws-neuronx-dkms-2.19.64.0.noarch.rpm" from upstream source

What I'd Like

This log message is clarified

Other options considered

Split the logic for force upstream and upstream fallback, such that in cases of packages specifying force-upstream = true, the lookaside cache is never consulted. This seems to be closer to the behavior that force-upstream implies