fix: select: remove toggle button from tab order

[jhoward-eightfold]

SUMMARY:

This removes focusability from the button in Select components. This resolves an accessibility and usability issue in which the Select component input is focusable in order to open the dropdown, and the button provides unnecessary duplication of that action.

GITHUB ISSUE (Open Source Contributors)

JIRA TASK (Eightfold Employees Only):

CHANGE TYPE:

• Bugfix Pull Request
• Feature Pull Request

TEST COVERAGE:

• Tests for this change already exist
• I have added unittests for this change

TEST PLAN:

• Pull down code
• run storybook
• confirm that select component still works as desired:
  • can open the dropdown while keyboard focused on the input
  • can open the dropdown by click on the input and/or the toggle button

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