Flaky test: command_runs_with_configured_cwd_and_resolves_relative_path fails with ETXTBSY

**Describe the bug**

The test
`providers::command_auth::tests::command_runs_with_configured_cwd_and_resolves_relative_path`
occasionally fails on Linux CI with:

```text
failed to run auth command './get-token.sh': Text file busy (os error 26)
```

Failed CI job:
https://github.com/aaif-goose/goose/actions/runs/34327955183/job/102389802174?pr=11944

The equivalent `rustls-tls` job passed, and rerunning the test succeeds, suggesting a filesystem-related race when the temporary script is created and immediately executed.

The test was introduced in #11657.

**To reproduce**

Run repeatedly on Linux:

```bash
cargo test -p goose --lib \
providers::command_auth::tests::command_runs_with_configured_cwd_and_resolves_relative_path
```

**Expected behavior**

The test should pass reliably in CI.

**Additional context**

A possible fix is to create the script under a temporary filename and atomically rename it before execution. The exact cause should be confirmed before implementation.

The failing test is in providers::command_auth::tests::command_runs_with_configured_cwd_and_resolves_relative_path. Look at the test file to see how the temporary script './get-token.sh' is created and executed. Investigate the race condition on Linux where the file is busy (ETXTBSY). A potential fix is to write to a temporary file and rename it atomically before execution. Run the test repeatedly to reproduce the flakiness.

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