Replaced deprecated reference to privateKeyAccount in login.ts

**Removed deprecated reference:** Update login.ts to use `privateKeyToAccount` instead of deprecated `privateKeyAccount`. 

From:
```
import { privateKeyAccount } from "thirdweb/wallets";
 
const thirdwebAuth = createAuth({
  domain: process.env.NEXT_PUBLIC_THIRDWEB_AUTH_DOMAIN || "",
  adminAccount: privateKeyAccount({ client, privateKey }),
  client: client,
});
```

To:
```
import { privateKeyToAccount } from "thirdweb/wallets";
 
const thirdwebAuth = createAuth({
  domain: process.env.NEXT_PUBLIC_THIRDWEB_AUTH_DOMAIN || "",
  adminAccount: privateKeyToAccount({ client, privateKey }),
  client: client,
});
```

Signed-off-by: Captain Unknown <[email protected]>

Author: CaptainUnknown

apps/portal/src/app/connect/auth/frameworks/next/page.mdx

@@ -226,7 +226,7 @@ Create an `actions` directory with a `login.ts` file with the following:
 ```tsx
 "use server";
 import { VerifyLoginPayloadParams, createAuth } from "thirdweb/auth";
-import { privateKeyAccount } from "thirdweb/wallets";
+import { privateKeyToAccount } from "thirdweb/wallets";
 import { client } from "@/lib/client";
 import { cookies } from "next/headers";
 
@@ -238,7 +238,7 @@ if (!privateKey) {
 
 const thirdwebAuth = createAuth({
 	domain: process.env.NEXT_PUBLIC_THIRDWEB_AUTH_DOMAIN || "",
-	adminAccount: privateKeyAccount({ client, privateKey }),
+	adminAccount: privateKeyToAccount({ client, privateKey }),
 	client: client,
 });