test: cover SSH daemon restart failure

[bobsingh-dev]

Proposed Commit Message

test: cover SSH daemon restart failure

Add unit test coverage for the SSH daemon restart failure path. Verify
that a ProcessExecutionError raised while restarting the SSH service is
handled and a warning is logged.

Additional Context

Adds test coverage for the existing error-handling behavior in
_restart_ssh_daemon. No production behavior is changed.

Test Steps

Run the relevant unit tests:

tox -e py3 -- tests/unittests/config/test_cc_set_passwords.py

Result: 49 tests passed.

Run formatting:

tox -e do_format

Run formatting, linting, and type checks:

tox -e check_format

All checks pass.

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits.