cephadm: black-format OSD key rotation code in daemons/ceph.py

The OSD keyring rotation changes from the CVE-2025-30156 cephx merge
(c9bc85adec3 "cephadm: restart OSD systemd unit after key rotation",
24dc65ef20d "cephadm: Add retries to OSD key rotation") added lines to
cephadmlib/daemons/ceph.py that are not formatted the way
`tox -e check-black` (black>=23,<24, -l78) expects, so run-tox-cephadm
fails on every PR now that the py3 env passes again:

  would reformat /ceph/src/cephadm/cephadmlib/daemons/ceph.py
  1 file would be reformatted, 50 files would be left unchanged.

This is the output of `tox -e format-black` (black 23.12.1) on that
file; no functional change.

Fixes: 24dc65ef20defe9761036f10527e7c5ccbe057bd
Signed-off-by: David Galloway <david.galloway@ibm.com>
Assisted-by: Claude Fable 5 (claude-fable-5)