Fix snapshot filtering for relative paths in the backup command

The snapshot filtering internally converts relative paths to absolute
ones to ensure that the parent snapshots selection works for backups of
relative paths.

internal/restic/snapshot_find.go

@@ -46,6 +46,7 @@ func (f *SnapshotFilter) findLatest(ctx context.Context, be Lister, loader Loade
 		}
 		absTargets = append(absTargets, filepath.Clean(target))
 	}
+	f.Paths = absTargets
 
 	var latest *Snapshot