`TestInitKeys` verified whether a host key file was regenerated by
comparing `os.FileInfo` before and after a `InitDefaultHostKeys` call.
On systems where the OS clock / filesystem timestamp granularity is
coarse, both writes land in the same tick and get an identical mtime.
The resulting `FileInfo` is then byte-for-byte equal even though the key
was actually regenerated, so `assert.NotEqual` fails.
Since a regenerated key always produces different random bytes,
comparing the content can reliably detect regeneration.
