fix(docs): outdated zkSync Era testnet contract verifier URL in zksync-era-tooling

[Sertug17]

Bug Report

docs/zksync-era-tooling.mdx contains a dead URL for the zkSync Era testnet contract verifier.

Affected File

docs/zksync-era-tooling.mdx line 60

Problem

Current:

verifyURL: "https://zksync2-testnet-explorer.zksync.dev/contract_verification",

The zksync2-testnet-explorer.zksync.dev subdomain is from the pre-rebrand zkSync 2.0 era and no longer resolves. zkSync Era testnet was migrated to zkSync Era Sepolia.

Suggested Fix

verifyURL: "https://explorer.sepolia.era.zksync.dev/contract_verification",

Verification

Confirmed the old URL is present at line 60 of zksync-era-tooling.mdx. The current zkSync Era Sepolia explorer is at explorer.sepolia.era.zksync.dev.