spurious failure from test_auth_login_double

[ahl]

Here's what I saw:

---- test_auth_login_double stdout ----
thread 'test_auth_login_double' panicked at cli/tests/test_auth.rs:400:5:
assertion failed: modes do not match for /var/folders/q4/wlt470150sn72ty0zyxxcng8003c85/T/.tmpBZiLqQ/config.toml
  expected: 0o644
    actual: 0o666
     umask: 0o022
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

I was on macOS; I've only seen this failure once.