fix(Indeterminate Checkbox): Improved accessibility for `Indeterminate status (#1231)

[olehnoskov-cengage]

Issue: #1231

What I did

Added aria-checked="mixed" to the Indeterminate checkbox when in the indeterminate status

Screenshots:

Checklist

• [x] changeset has been added
• [x] Pull request description is descriptive
• [ ] I have made corresponding changes to the documentation
• [x] New and existing unit tests pass locally with my changes
• [ ] I have added tests that prove my fix is effective or that my feature works

How to test

Open the storybook the Indeterminate Checkbox section Confirm new aria-checked property for Indeterminate checkbox

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: d254c5e80e6fabff0f5eae2a04dc4c88e984c35c

The changes in this PR will be included in the next version bump.

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[olehnoskov-cengage]

fix(Indeterminate Checkbox): Improved accessibility for `Indeterminate status (#1231)