alternative way to check if file is executable

just fyi this might be another way (better? dunno)

https://stackoverflow.com/a/41929624/1223975

```js
const fs = require('fs');

fs.access('./foobar.sh', fs.constants.X_OK, (err) => {
console.log(err ? 'cannot execute' : 'can execute');
});
```

Review the linked Stack Overflow example and compare its fs.access(..., fs.constants.X_OK, ...) behavior with the repository's current executable check. Decide whether the alternative should replace the existing approach, then add or update coverage for the chosen behavior.

索引モデルが issue の本文から書いたものです。