storySort does use V6 compatibility mode for both build and dev

[seanmcintyre]

Using 6.4.0-beta.30.

---

To Reproduce

Using in main.js:

  features: {
    postcss: false,
    previewCsfV3: false,
    buildStoriesJson: true,
    storyStoreV7: false,
  }

running storybook dev with a storySort function that is written in V7 style yields this console error:
Are you using a V7-style sort function in V6 compatibilty mode?

building storybook with a storySort function that is written in V6 style yields this CLI error:
Are you using a V6-style sort function in V7 mode?

---

System

  System:
    OS: macOS 11.6
    CPU: (16) x64 Intel(R) Core(TM) i9-9980HK CPU @ 2.40GHz
  Binaries:
    Node: 14.17.3 - ~/.nvm/versions/node/v14.17.3/bin/node
    Yarn: 1.22.4 - ~/.yarn/bin/yarn
    npm: 6.14.13 - ~/.nvm/versions/node/v14.17.3/bin/npm
  Browsers:
    Chrome: 95.0.4638.69
    Firefox: 93.0
    Safari: 15.0
  npmPackages:
    @storybook/addon-a11y: 6.4.0-beta.30 => 6.4.0-beta.30 
    @storybook/addon-essentials: 6.4.0-beta.30 => 6.4.0-beta.30 
    @storybook/addon-postcss: ^2.0.0 => 2.0.0 
    @storybook/addon-storysource: 6.4.0-beta.30 => 6.4.0-beta.30 
    @storybook/builder-webpack5: 6.4.0-beta.30 => 6.4.0-beta.30 
    @storybook/components: 6.4.0-beta.30 => 6.4.0-beta.30 
    @storybook/manager-webpack5: 6.4.0-beta.30 => 6.4.0-beta.30 
    @storybook/react: 6.4.0-beta.30 => 6.4.0-beta.30 
    @storybook/theming: 6.4.0-beta.30 => 6.4.0-beta.30 

---

Minor aside!

The console error: Are you using a V7-style sort function in V6 compatibilty mode? has a typo. "compatibilty" is misspelled.

[seanmcintyre]

Setting buildStoriesJson: false helped resolve the error, but my storySort function is now being ignored.

[shilman]

@seanmcintyre do you happen to have a reproduction handy? If not, can you create one? See how to create a repro. Thank you! 🙏

[shilman]

Boo-yah!! I just released https://github.com/storybookjs/storybook/releases/tag/v6.4.0-rc.4 containing PR #16724 that references this issue. Upgrade today to the @next NPM tag to try it out!

npx sb upgrade --prerelease

Closing this issue. Please re-open if you think there's still more to do.