fix: missing non-evm account modal bottom border-radius (#31374)

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## **Description**

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

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## **Related issues**

Fixes:

## **Manual testing steps**

1. Go to this page...
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## **Screenshots/Recordings**

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### **Before**

![CleanShot 2025-03-27 at 17 24
13@2x](https://github.com/user-attachments/assets/f14af6b8-db9e-4359-9733-8a1c30f22447)


### **After**

![CleanShot 2025-03-27 at 17 25
53@2x](https://github.com/user-attachments/assets/26498829-0607-4eb0-8aa2-255c91bed483)


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Author: digiwand

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

@@ -12,7 +12,6 @@ import {
   ButtonPrimarySize,
 } from '../../../component-library';
 import {
-  BackgroundColor,
   BlockSize,
   Display,
   FlexDirection,
@@ -44,7 +43,6 @@ const AddNonEvmAccountModal = ({ chainId }: { chainId: CaipChainId }) => {
       </Box>
       <Box
         className="add-non-evm-account-modal__footer"
-        backgroundColor={BackgroundColor.backgroundDefault}
         padding={4}
         width={BlockSize.Full}
       >