"npm init gatsby" w/ theme-ui fails to start as it requires emotion/mdx

[KyleAMathews]

Preliminary Checks

• This issue is not a duplicate. Before opening a new issue, please search existing issues: https://github.com/gatsbyjs/gatsby/issues
• This issue is not a question, feature request, RFC, or anything other than a bug report directly related to Gatsby. Please post those things in GitHub Discussions: https://github.com/gatsbyjs/gatsby/discussions

Description

gatsby-plugin-theme-ui requires @emotion/react @emotion/styled @mdx-js/react to be installed as well.

Reproduction Link

n/a

Steps to Reproduce

1. npm init gatsby
2. select "theme-ui" as the styling option
3. run npm run develop
4. the develop server fails to start
   ...

Expected Result

The develop server starts

Actual Result

It didn't

Environment

n/a

Config Flags

No response