.NET Docs - Synchronous EngineWallet.Create (#6469)

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## PR-Codex overview
This PR focuses on modifying the instantiation of the `engineWallet` variable by removing the `await` keyword, indicating a change in how the `EngineWallet.Create` method is called.

### Detailed summary
- Changed `var engineWallet = await EngineWallet.Create(` to `var engineWallet = EngineWallet.Create(`.
- This change suggests that `EngineWallet.Create` no longer returns a promise or that the method is being called synchronously.

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Author: 0xFirekeeper

apps/portal/src/app/dotnet/wallets/providers/engine-wallet/page.mdx

@@ -16,7 +16,7 @@ Instantiate a `Engine` with a given private key. This wallet is capable of signi
 
 ```csharp
 // EngineWallet is compatible with IThirdwebWallet and can be used with any SDK method/extension
-var engineWallet = await EngineWallet.Create(
+var engineWallet = EngineWallet.Create(
     client: client,
     engineUrl: Environment.GetEnvironmentVariable("ENGINE_URL"),
     authToken: Environment.GetEnvironmentVariable("ENGINE_ACCESS_TOKEN"),