Lit / esbuild doesn't work with latest gts

I'm working on a web application built with [Lit](http://lit.dev/) and [esbuild](https://esbuild.github.io/).
It was functioning correctly with `gts@5.3.1`, but broke after upgrading to `gts@6.0.2`.

Demo:
https://stackblitz.com/edit/stackblitz-starters-yvbnm5rc

Steps to reproduce:
- run `npm i`
- run `npx http-server build` and see the preview where no string is rendered.
- downgrade `gts` to `5.3.1`
- run `npm i `
- run `npx http-server build` and see the preview where "hello world" is rendered.