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)

Affected packages and versions

8.0.2

Link to runnable example

https://codesandbox.io/s/nice-austin-wrug0t

Steps to reproduce

1. Install remark-code-frontmatter
2. Install remark-code-extra
3. Configure the component to use both plugins
4. See error

Expected behavior

The render still works.

Actual behavior

When using the remark-code-frontmatter and remark-code-extra plugins, I'm getting the following error:

index.js:566 Uncaught (in promise) Error: `runSync` finished async. Use `run` instead
    at assertDone (index.js:566)
    at Function.runSync (index.js:352)
    at ReactMarkdown (react-markdown.js:107)
    at renderWithHooks (react-dom.development.js:14985)
    at mountIndeterminateComponent (react-dom.development.js:17811)
    at beginWork (react-dom.development.js:19049)
    at HTMLUnknownElement.callCallback (react-dom.development.js:3945)
    at Object.invokeGuardedCallbackDev (react-dom.development.js:3994)
    at invokeGuardedCallback (react-dom.development.js:4056)
    at beginWork$1 (react-dom.development.js:23964)

Digging in, it looks like the remark-code-extra plugin is returning Promises, forcing the async flow.

Runtime

No response

Package manager

No response

OS

No response

Build and bundle tools

No response