addons-actions is not working with addons-docs mdx format story

[jacklimwenjie]

Describe the bug
addons-actions failed to be triggered when in a mdx format of story

To Reproduce
Steps to reproduce the behavior:

1. Setup a Storybook with addons-actions and addons-docs.
2. Create a story with mdx format.
3. Try to use addon-actions in the story. For example:

<Story name="basic">
  <Button
    onClick={action("onClick")}
  />
</Story>

4. When the button is clicked, the action is not logged.

Expected behavior
addon-actions should be able to be triggered in mdx format story like CSF story or story created using old API.

System:

Environment Info:

  System:
    OS: macOS 10.15.1
    CPU: (4) x64 Intel(R) Core(TM) i5-7360U CPU @ 2.30GHz
  Binaries:
    Node: 12.12.0 - /usr/local/bin/node
    Yarn: 1.19.1 - /usr/local/bin/yarn
    npm: 6.11.3 - /usr/local/bin/npm
  Browsers:
    Chrome: 78.0.3904.87
    Safari: 13.0.3
  npmPackages:
    @storybook/addon-actions: ^4.0.0||^5.0.0||5.2.0-beta.13 => 5.2.5 
    @storybook/addon-docs: ^5.2.5 => 5.2.5 
    @storybook/addon-knobs: ^5.2.5 => 5.2.5 
    @storybook/react: ^5.2.5 => 5.2.5 

[shilman]

@jacklimwenjie When the story is viewed in the canvas tab, an action is logged. E.g. https://storybookjs.now.sh/official-storybook/?path=/story/addons-docs-mdx--hello-story

When the story is viewed in the docs tab, it is not, which is a special case of #6700