Describe the bug

When using DuplicatePackageCheckerPlugin with the latest version 0.6.0-alpha.4 and "@emotion/react": "^11.1.4" and "@emotion/styled": "^11.0.0" I'm seeing:

warn  - @emotion/is-prop-valid
  Multiple versions of @emotion/is-prop-valid found:
    0.8.8 ./~/@emotion/is-prop-valid
    1.0.0 ./~/@emotion/styled/~/@emotion/is-prop-valid

To Reproduce

Add https://github.com/darrenscerri/duplicate-package-checker-webpack-plugin to the project using Theme UI and try building.

Expected behavior

No duplicated packages should be added to the bundle.

Additional context

➜ npx npm-why @emotion/is-prop-valid

  Who required @emotion/is-prop-valid:

  monolisa-website > theme-ui > @theme-ui/components > @styled-system/should-forward-prop > @emotion/is-prop-valid@0.8.8

so it looks like it's coming from styled-system which is a dependency of Theme UI and probably needs to be updated there.