Fix tempfile leak in behave test suite

[rolandwalker]

Description

Fix tempfile leak in behave test suite, preferring NamedTemporaryFile over mkstemp.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[github-actions]

1. Cleanup can still leak temp files on failure path (low)

• In test/test_config.py:113, deletion happens only after the assertion succeeds.
• If get_mylogin_cnf_path() returns unexpected output and the assert at line 116 fails, cleanup at lines 118-122 never runs, so the temp file leaks (the exact issue this PR is trying to address).
• Action: wrap the assertion block in try/finally (or use tmp_path) and do unconditional cleanup in finally; avoid swallowing cleanup errors with print.

No security issues found in this PR diff.

Testing gap:

• I could not run tests in this environment because pytest is not installed (pytest: command not found), so runtime verification is pending.