FV-ANC-3-CL9 Using ctx.remaining_accounts without manual discriminator check

Bad

let extra_account = &ctx.remaining_accounts[0];
// No check for account type discriminator.

Good

let extra_account = &ctx.remaining_accounts[0];
let data = extra_account.try_borrow_data()?;
if &data[..8] != MyAccountType::DISCRIMINATOR {
    return Err(ProgramError::InvalidAccountData);
}