This matches how the `buck2-lsp` works for that extension.

Fixes https://github.com/zaucy/zed-starlark/issues/18

Before you mark this PR as ready for review, make sure that you have:
- [ ] (n/a) Added a solid test coverage and/or screenshots from doing
manual testing
- [x] Done a self-review taking into account security and performance
aspects
- [x] Aligned any UI changes with the [UI
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)

Release Notes:

- N/A