A user reported to me that they are unable to create a PSBT with a legacy watchonly wallet when they use the GUI. They get an error "The amount exceeds your balance".

I think the issue is that the GUI will retrieve the wallet's balance via `AvailableCoins` before calling `CreateTransaction`. This call to `AvailableCoins` is resulting in fewer coins being returned with recent changes to how `AvailableCoins` works, particularly with additional filtering of spendable coins and preset coins.

***

Note that this does not effect descriptor wallets. A workaround for this issue is to switch to using descriptor wallets. An existing legacy wallet can be turned into a descriptor wallet using the `migratewallet` RPC. However many watchonly legacy wallets are likely the result of importing descriptors via `importmulti`. For such wallets, I recommend creating a new descriptor wallet and re-importing the descriptors.
{
    const auto test_setup = MakeNoLogFileContext<const TestingSetup>();
    CWallet wallet{test_setup->m_node.chain.get(), "", CreateMockWalletDatabase()};
    {
        LOCK(wallet.cs_wallet);
        wallet.SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
        wallet.SetupDescriptorScriptPubKeyMans();
        if (wallet.LoadWallet() != DBErrors::LOAD_OK) assert(false);
    }
    
    CScript dest = GetScriptForDestination(getNewDestination(wallet, output_type));
    
    const auto& params = Params();
    unsigned int chain_size = 5000; 
    for (unsigned int i = 0; i < chain_size; ++i) {
        generateFakeBlock(params, test_setup->m_node, wallet, dest);
    }
    
    auto bal = wallet::GetAvailableBalance(wallet); 
    assert(bal == 50 * COIN * (chain_size - COINBASE_MATURITY));
    wallet::CCoinControl coin_control;
    coin_control.m_allow_other_inputs = allow_other_inputs;
    CAmount target = 0;
    if (preset_inputs) {