Bugfix: fix metadata errors during backup of removable disks on Windows

Since restic 0.17.0, backups of removable disks on Windows could report
errors with retrieving metadata like shown below.

```
error: incomplete metadata for d:\filename: get named security info failed with: Access is denied.
```

This has now been fixed.

https://github.com/restic/restic/issues/5003
https://github.com/restic/restic/pull/5123
https://forum.restic.net/t/backing-up-a-folder-from-a-veracrypt-volume-brings-up-errors-since-restic-v17-0/8444