--symlink-install ignores build_scripts executable option in setup.py

if I add a
```
    options={
        'build_scripts': {
            'executable': '/usr/bin/env python3',
        },
    },
```

to the `setup.py`, then I get all my `console_scripts` with a lovely `#!/usr/bin/env python3` shebang when I `colcon build` without `--symlink-install`

But if I add `--symlink-install` to the `colcon build` command, the shebang returns to being `#!/usr/bin/python3`
