Merge pull request #9383 from baker-travis/knob-groups-overflow-not-scrolling

[baker-travis]

fixes #9299

Issue:

What I did

Allowed the overflow of the container holding the knob categories.

How to test

1. Use the official-storybook example project
2. Navigate to Addons -> Knobs -> withKnobs -> tweaks static values organized in groups.
3. Move the panel that contains "Knobs" to the right side of your screen.
4. Observe that you can now scroll the knob categories.

• Is this testable with Jest or Chromatic screenshots? No
• Does this need a new example in the kitchen sink apps? No
• Does this need an update to the documentation? No

If your answer is yes to any of these, please make sure to include it in your PR.

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[ndelangen]

Thank you @baker-travis !

[ndelangen]

@baker-travis would you be able to resolve the merge conflicts? Would love to merge this in.

[baker-travis]

@ndelangen Updated the branch, should be good to go now.

[ndelangen]

Thanks!