Bugfix: Fix spurious "A Required Privilege Is Not Held by the Client" error

On Windows, creating a backup could sometimes trigger the following error:

```
error: nodeFromFileInfo [...]: get named security info failed with: a required privilege is not held by the client.
```

This has now been fixed.

https://github.com/restic/restic/issues/5004
https://github.com/restic/restic/pull/5019
