fix: missing non-evm account modal bottom border-radius

[digiwand]

Description

Removes .add-non-evm-account-modal__footer background-color to allow its parent background-color with border-radius applied

Related issues

Fixes:

Manual testing steps

1. Go to this page...

Screenshots/Recordings

Before

After

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• I've followed MetaMask Contributor Docs and MetaMask Extension Coding Standards.
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Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
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[github-actions]

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[metamaskbot]

✨ Files requiring CODEOWNER review ✨

🖥️ @MetaMask/wallet-ux

• ui/components/multichain/network-list-menu/add-non-evm-account/add-non-evm-account.tsx

[vinnyhoward]

LGTM!