stack_snapshot ignores stack warning about missing Cabal file in archive overrides

[aherrmann]

Describe the bug
Using a local snapshot to point to an archive URL or specific Github commit/fork will silently ignore the override and still use the Hackage version of the underlying resolver if the new archive does not include a Cabal file.

Specifically, stack ls dependencies json --global-hints --external will print out a warning of the form

DEPRECATED: The package at Archive from https://github.com/fpco/unliftio/archive/de13c448e4b77e8ce318b78445e17f6c20003325.tar.gz in subdir unliftio does not include a cabal file.
Instead, it includes an hpack package.yaml file for generating a cabal file.
This usage is deprecated; please see https://github.com/commercialhaskell/stack/issues/5210.
Support for this workflow will be removed in the future.

But, it will still return exit code 0 and ignore the archive override and stack_snapshot does not notice that something went wrong.

To Reproduce

1. Use a local Stackage snapshot of the form

   resolver: nightly-2022-06-10
   packages:
     - github: "fpco/unliftio"
       commit: de13c448e4b77e8ce318b78445e17f6c20003325
       subdirs:
         - unliftio-core
         - unliftio
   

   and add unliftio-core to the packages attribute of stack_snapshot.
2. Repin the snapshot repository.
3. Inspect the generated lock-file and observe that unliftio-core is still fetched from Hackage instead of Github at commit de13c448.

Expected behavior
If stack cannot provide the requested override in a custom snapshot, then stack_snapshot fetch/pin should fail with a clear error message, instead of silently ignoring the issue.

Environment

• OS name + version: Ubuntu 21.10
• Bazel version: 4.2.1
• Version of the rules: b8ac6c1

Additional context
commercialhaskell/stack#5210 points out that repositories should contain a Cabal file.