message: Update wallet passphrase help info for staking.
diff: @@ -2319,6 +2319,7 @@ UniValue walletpassphrase(const JSONRPCRequest& request)
  "\nArguments:\n"
  "1. \"passphrase\" (string, required) The wallet passphrase\n"
  "2. timeout (numeric, required) The time to keep the decryption key in seconds.\n"
  + "3. staking (bool, optional, default=false) Unlock wallet for staking only.\n"
  "\nNote:\n"
  "Issuing the walletpassphrase command while the wallet is already unlocked will set a new unlock\n"
  "time that overrides the old one.\n"
  