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.

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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.
{
    auto tip = WITH_LOCK(::cs_main, return context.chainman->ActiveTip());
    return (tip) ? TipBlock{tip->GetBlockHash(), tip->GetBlockTime(), tip->nHeight} :
           TipBlock{params.GenesisBlock().GetHash(), params.GenesisBlock().GetBlockTime(), 0};
}
void generateFakeBlock(const CChainParams& params,
                       const node::NodeContext& context,
                       CWallet& wallet,
                       const CScript& coinbase_out_script)
{
    TipBlock tip{getTip(params, context)};
    
    CBlock block;
    CMutableTransaction coinbase_tx;
    coinbase_tx.vin.resize(1);
    coinbase_tx.vin[0].prevout.SetNull();