fix: make it work when a default lang was specified

[dargmuesli]

Description

Resolved merge conflicts for #65.

---

<template lang="html">
  <div>foo</div>
</script>

and

<script setup lang="js">
const foo = 'foo'
</script>

didn't work.
This PR fixes these.

requires vuejs/core#7388
fixes #17

Additional context

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[sapphi-red]

Thank you!