devcontainer up fails with unclear error when specifying non-existent remoteUser

When creating a devcontainer with a removeUser that does not exist in the container, `devcontainer up` fails without a clear error

The log output contains
```
Shell server terminated (code: 126, signal: null)
no users found
```
for one of the commands and exits with a generic error message in the final result. We use `--log-format=json`, and those lines are plain text, so aren't getting parsed and shown in the build output

## To reproduce

Can reproduce with the following `devcontainer.json`:

```
{
"image": "mcr.microsoft.com/vscode/devcontainers/python:3.10-bullseye",
"remoteUser": "foobar"
}
```

Logs:

```
$ devcontainer up --workspace-folder . --config .devcontainer/devcontainer.json --log-format=json
...
{"type":"start","level":2,"timestamp":1744618710700,"text":"Run: docker inspect --type container 240a168268e3"}
{"type":"stop","level":2,"timestamp":1744618710714,"text":"Run: docker inspect --type container 240a168268e3","startTimestamp":1744618710700}
{"type":"start","level":2,"timestamp":1744618710715,"text":"Inspecting container"}
{"type":"start","level":2,"timestamp":1744618710715,"text":"Run: docker inspect --type container 240a168268e39df374572d62dce4ff61599028711968f99e66c14d248f5a1fe7"}
{"type":"stop","level":2,"timestamp":1744618710731,"text":"Run: docker inspect --type container 240a168268e39df374572d62dce4ff61599028711968f99e66c14d248f5a1fe7","startTimestamp":1744618710715}
{"type":"stop","level":2,"timestamp":1744618710731,"text":"Inspecting container","startTimestamp":1744618710715}
{"type":"start","level":2,"timestamp":1744618710732,"text":"Run in container: /bin/sh"}
{"type":"start","level":2,"timestamp":1744618710734,"text":"Run in container: uname -m"}
{"type":"stop","level":2,"timestamp":1744618710753,"text":"Run in container: /bin/sh","startTimestamp":1744618710732}
Shell server terminated (code: 126, signal: null)
no users found

{"type":"start","level":2,"timestamp":1744618710754,"text":"Run in container: (command -v getent >/dev/null 2>&1 && getent passwd 'foobar' || grep -E '^foobar|^[^:]*:[^:]*:foobar:' /etc/passwd || true)"}
{"type":"text","level":2,"timestamp":1744618710754,"text":"Stdin closed!"}
Error: An error occurred setting up the container.
at D6 (/usr/local/lib/node_modules/@devcontainers/cli/dist/spec-node/devContainersSpecCLI.js:467:1253)
at Ix (/usr/local/lib/node_modules/@devcontainers/cli/dist/spec-node/devContainersSpecCLI.js:467:997)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at async H6 (/usr/local/lib/node_modules/@devcontainers/cli/dist/spec-node/devContainersSpecCLI.js:484:3842)
at async BC (/usr/local/lib/node_modules/@devcontainers/cli/dist/spec-node/devContainersSpecCLI.js:484:4957)
at async d7 (/usr/local/lib/node_modules/@devcontainers/cli/dist/spec-node/devContainersSpecCLI.js:665:202)
at async f7 (/usr/local/lib/node_modules/@devcontainers/cli/dist/spec-node/devContainersSpecCLI.js:664:14804)
at async /usr/local/lib/node_modules/@devcontainers/cli/dist/spec-node/devContainersSpecCLI.js:484:1188
{"outcome":"error","message":"An error occurred setting up the container.","description":"An error occurred setting up the container.","containerId":"240a168268e39df374572d62dce4ff61599028711968f99e66c14d248f5a1fe7"}
```

devcontainer CLI version: `0.75.0`
OS: `Ubuntu 24.04.2 LTS`
Docker version: `Docker version 27.5.1, build 9f9e405`