fix: relax network symbol length validation (#11693)

## **Description**

When adding a network with wallet_addEthereumChain, MetaMask was
requiring the chain's symbol to be minimum of 2 characters. But there
are networks with single character symbols.

## **Related issues**

- Equivalent PR on extension:
MetaMask/metamask-extension#24872
-  #11217

## **Manual testing steps**



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- [ ] I've completed the PR template to the best of my ability
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Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

app/core/RPCMethods/lib/ethereum-chain-utils.js

@@ -155,9 +155,9 @@ function validateNativeCurrency(nativeCurrency) {
   }
   const ticker = nativeCurrency?.symbol || 'ETH';
 
-  if (typeof ticker !== 'string' || ticker.length < 2 || ticker.length > 6) {
+  if (typeof ticker !== 'string' || ticker.length < 1 || ticker.length > 6) {
     throw rpcErrors.invalidParams({
-      message: `Expected 2-6 character string 'nativeCurrency.symbol'. Received:\n${ticker}`,
+      message: `Expected 1-6 character string 'nativeCurrency.symbol'. Received:\n${ticker}`,
     });
   }