errors, fs: Replace CombineErrors with stdlib Join

This does not produce exactly the same messages, as it inserts newlines
instead of "; ". But given how long our error messages can be, that
might be a good thing.

internal/fs/node_windows.go

@@ -189,7 +189,7 @@ func nodeRestoreGenericAttributes(node *restic.Node, path string, warn func(msg
 	}
 
 	restic.HandleUnknownGenericAttributesFound(unknownAttribs, warn)
-	return errors.CombineErrors(errs...)
+	return errors.Join(errs...)
 }
 
 // genericAttributesToWindowsAttrs converts the generic attributes map to a WindowsAttributes and also returns a string of unknown attributes that it could not convert.