local: mark repository files as read-only

This is intended to prevent accidental modifications of data files.
Marking the files as read-only was accidentally removed in #1258.

internal/backend/local/local_windows.go

@@ -7,6 +7,6 @@ import (
 // We don't modify read-only on windows,
 // since it will make us unable to delete the file,
 // and this isn't common practice on this platform.
-func setNewFileMode(f string, mode os.FileMode) error {
+func setFileReadonly(f string, mode os.FileMode) error {
 	return nil
 }