feat(builder): make bundle executable

[paul-soporan]

What's the problem this PR addresses?

The builder doesn't make the bundle executable, which means that it can't be spawned directly without node.

I noticed this while testing the yarn bench script in our repo, which symlinks the bundle and then tries to spawn it without first chmod-ing it.

I decided that it makes sense for the builder to chmod it directly.

How did you fix it?

Made the builder chmod it.

Checklist

• I have read the Contributing Guide.

• I have set the packages that need to be released for my changes to be effective.

• I will check that all automated PR checks pass before the PR gets reviewed.