fix(list): remove uneeded border radius from items in inset list

[amandaejohnston]

Issue number: N/A

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What is the current behavior?

In MD mode, items in an inset list currently receive their own border radius, separate from the border radius also applied to the inset list itself. The original intent was likely to ensure that the corners of the items don't spill out of the list. However, the item's border radius is no longer needed, for two reasons:

1. MD has since added top/bottom padding to their lists (spec), which we've mirrored. This means the borders no longer line up anyway.
2. Even if a developer removes the list's vertical padding (we set it on the host here, so it's easy to overwrite), inset lists currently have overflow: hidden set here, so the list's border radius still applies correctly even with the items' border radius removed.

What is the new behavior?

Item border radius in inset lists removed.

When testing locally, you may find it useful to increase the MD border radius value here so it's easier to see.

Does this introduce a breaking change?

• Yes
• No

Other information

[liamdebeasi]

Looks good! I would consider this a fix though since it's removing buggy behavior.