Add `micromark-util-types` as a dependency

[arcanis]

Initial checklist

• [x] I read the support docs
• [x] I read the contributing guide
• [x] I agree to follow the code of conduct
• [x] I searched issues and couldn’t find anything (or linked relevant results below)
• [x] If applicable, I’ve added docs and tests

Description of changes

Various type imports directly reference micromark-util-types: https://github.com/micromark/micromark-extension-frontmatter/blob/07a4d981df602f558f05cd8bafe1be4b57fea072/dev/lib/syntax.js#L2-L6

Since it isn't listed in the dependencies, loose package managers like npm may generate incorrect hoisting (so TS would resolve the wrong version of micromark-util-types), and strict package managers like Yarn or pnpm may cause TS to fail to resolve the dependency.

This diff simply adds the missing dependency.

[github-actions[bot]]

Hi! It seems some of the things asked in the template are missing? Please edit your post to fill out everything.

• [ ] Initial checklist (todo)
• [x] Description of changes

You won’t get any more notifications from me, but I’ll keep on updating this comment, and remove it when done!

If you need it, here’s the original template

```markdown ### Initial checklist * [ ] I read the support docs * [ ] I read the contributing guide * [ ] I agree to follow the code of conduct * [ ] I searched issues and couldn’t find anything (or linked relevant results below) * [ ] If applicable, I’ve added docs and tests ### Description of changes TODO ```

Thanks, — bb

[arcanis]

The typecheck errors look unrelated to the PR itself 🤔

[wooorm]

This looks good, thanks! TS is indeed unrelated. I’ll get back to the repo in ±10 days as I’m on holiday. OK?

[github-actions[bot]]

Hi! This was closed. Team: If this was merged, please describe when this is likely to be released. Otherwise, please add one of the no/* labels.

[wooorm]

Thanks, released in 1.0.1!