thrown value in `inspectDockerImage` obfuscates the underlying issue

The thrown value here (`err` instead of `_err`) obfuscates any error from the pull in the final result. The real error will be higher up in the logs, but it might be more helpful (especially in the codespaces case) to throw the result of the 'pull'. Eg:
```
Error response from daemon: Get \"https://mcr.microsoft.com/v2/\": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)\r\n`
```

https://github.com/devcontainers/cli/blob/efb3ffca505e252a58d8bf4d48da5ffe4becf0e2/src/spec-node/utils.ts#L237