fix: correct radio corner radius value

[chrisdholt]

Description

This PR corrects the visual design of the FAST radios.

Motivation & context

Somewhere between v2 and v3 of the homepage design specs, the corner radius for the radio buttons shifted to align with checkboxes. From a visual design standpoint, this is incorrect. Further, from an accessibility standpoint, this is even more problematic. The controls appear to the be same and have no distinct difference; this PR corrects the radios to be circular at all times solving both the visual design problem and the accessibility issue presented by this appearing the same as a checkbox.

Issue type checklist

• Chore: A change that does not impact distributed packages.
• Bug fix: A change that fixes an issue, link to the issue above.
• New feature: A change that adds functionality.

Is this a breaking change?

• This change causes current functionality to break.

Adding or modifying component(s) in @microsoft/fast-components checklist

• I have added a new component
• I have modified an existing component
• I have updated the definition file
• I have updated the configuration file

Process & policy checklist

• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

[EisenbergEffect]

Is it better to do

[marjonlynch]

looks good to me