Documentation for extending theme is wrong. Module Augmentation does not work.

In https://mui.com/customization/theming/#custom-variables the docs tell you to use following example to extend typescript type but it is not working:

declare module '@mui/material/styles' {
  interface Theme {
    status: {
      danger: string;
    };
  }
  // allow configuration using `createTheme`
  interface ThemeOptions {
    status?: {
      danger?: string;
    };
  }
}

• The issue is present in the latest release.
• I have searched the issues of this repository and believe that this is not a duplicate.

Current Behavior 😯

Current example in docs does not work.

Expected Behavior 🤔

Example should work.

Steps to Reproduce 🕹

Follow the docs.

The following type does work instead:

declare module "@mui/material/styles/createTheme" {
    interface Theme {
        test: string,
    }
    // allow configuration using `createMuiTheme`
    interface ThemeOptions {
        test?: string;
    }
}

Your Environment 🌎

   System:
    OS: Linux 5.10 Ubuntu 20.04.2 LTS (Focal Fossa)
  Binaries:
    Node: 14.17.5 - /usr/bin/node
    Yarn: 1.22.11 - /usr/local/bin/yarn
    npm: 7.24.1 - /usr/bin/npm