node: report error on xattr retrieval using standard error logging

internal/fs/interface.go

@@ -48,5 +48,5 @@ type File interface {
 	// ToNode returns a restic.Node for the File. The internally used os.FileInfo
 	// must be consistent with that returned by Stat(). In particular, the metadata
 	// returned by consecutive calls to Stat() and ToNode() must match.
-	ToNode(ignoreXattrListError bool) (*restic.Node, error)
+	ToNode(ignoreXattrListError bool, warnf func(format string, args ...any)) (*restic.Node, error)
 }