backend/local: Ignore ENOTTY for fsync on Mac

Fixes #4016.

internal/backend/local/local_windows.go

@@ -7,6 +7,9 @@ import (
 // Can't explicitly flush directory changes on Windows.
 func fsyncDir(dir string) error { return nil }
 
+// Windows is not macOS.
+func isMacENOTTY(err error) bool { return false }
+
 // 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.