bug: Fixed contrast of Show Info button in addon-info

[trevoreyre]

Issue: #6256

What I did

Updated the background color of the Show Info button so it passes accessibility checks from addon-a11y.

How to test

• Is this testable with Jest or Chromatic screenshots?
• Does this need a new example in the kitchen sink apps?
• Does this need an update to the documentation?

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

[Keraito]

LGTM, but can you provide a screenshot of the new color or that the a11y report doesn't fail anymore for verifications?

[codecov]

Codecov Report

Merging #6301 into next will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             next    #6301   +/-   ##
=======================================
  Coverage   38.29%   38.29%           
=======================================
  Files         648      648           
  Lines        9839     9839           
  Branches      387      387           
=======================================
  Hits         3768     3768           
  Misses       6011     6011           
  Partials       60       60

Impacted Files	Coverage Δ
addons/info/src/components/Story.js	88.34% <ø> (ø)	⬆️

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[trevoreyre]

@Keraito No problem. Here's the color before, with accessibility violations.

And here's after, with no violations.

[shilman]

Thanks @trevoreyre ! Looks great 👍