Suppress warnings from is_executable

[bytestream]

The code was recently changed in 1f07ae6

Every other is_executable() call suppresses warnings. I believe it should here too. Otherwise it outputs:

is_executable(): open_basedir restriction in effect. File(/usr/bin/tar) is not within the allowed path(s): (/Users/bytestream)

[github-actions]

Thanks for your pull request! We love contributions.

However, you should instead open a pull request on the main repository:

https://github.com/symfony/symfony

This repository is what we call a "subtree split": a read-only subset of that main repository.

We're looking forward to your PR there!