fix: accordion: ensure expand button props are passed down to the button

[dkilgore-eightfold]

SUMMARY:

• Fixes issue where the prop was not being referenced as intended

JIRA TASK (Eightfold Employees Only):

ENG-84999

CHANGE TYPE:

• [x] Bugfix Pull Request
• [ ] Feature Pull Request

TEST COVERAGE:

• [x] Tests for this change already exist
• [ ] I have added unittests for this change

TEST PLAN:

Pull the PR branch and run yarn and yarn storybook. Verify the Accordion story behaves as expected.

[codesandbox-ci[bot]]

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