Resolve #529 - className is now accepted by Panel.Section

[jonambas]

Closes #529

What Changed

• Passes className to Panel.Section

How To Test or Verify

• Run storybook and visit the Panel story with multiple sections
• Verify the className is in the DOM

PR Checklist

• Add the correct type label
• Pull request approval from #uxfe or #design-guild

[codecov]

Codecov Report

Merging #531 into main will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #531   +/-   ##
=======================================
  Coverage   93.26%   93.26%           
=======================================
  Files         118      118           
  Lines        1560     1560           
=======================================
  Hits         1455     1455           
  Misses        105      105           

Impacted Files	Coverage Δ
packages/matchbox/src/components/Panel/Section.js	100.00% <ø> (ø)

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[logansparlin]

Looks good