Save revocation file as only readable and writeable as user (600 permission)
The revocation file stored in the account storage (#477+) is readable by everyone on the system, and can therefore be sent by anyone who has access to this file to revoke the corresponding identity.
In the same vein as #420+ for the authentication files, let’s save the revocation file with `600` permissions (read and write for the user).
- https://github.com/astral-sh/ruff/issues/7620
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