Merge bitcoin-core#850: psbt: Use SIGHASH_DEFAULT when signing PSBTs

3e97ff9 gui, psbt: Use SIGHASH_DEFAULT when signing PSBTs (Ava Chow)

Pull request description:

  SIGHASH_DEFAULT should be used to indicate SIGHASH_DEFAULT for taproot inputs, and SIGHASH_ALL for all other input types. This avoids adding an unnecessary byte to the end of all Taproot signatures added to PSBTs signed in the GUI.

  See also bitcoin/bitcoin#22514

ACKs for top commit:
  Sjors:
    utACK 3e97ff9
  pablomartin4btc:
    utACK 3e97ff9
  hebasto:
    ACK 3e97ff9, I have reviewed the code and it looks OK.

Tree-SHA512: f96f26b3a6959865cf23039afb5ffb7e454fb52ee39c510583851caf00a8a383cde69bc7e90db536addbdd498a02f4b001cbaf509d6d53c5f8601b3933786f6c

Author: hebasto

src/qt/psbtoperationsdialog.cpp

@@ -83,7 +83,7 @@ void PSBTOperationsDialog::signTransaction()
 
     WalletModel::UnlockContext ctx(m_wallet_model->requestUnlock());
 
-    const auto err{m_wallet_model->wallet().fillPSBT(SIGHASH_ALL, /*sign=*/true, /*bip32derivs=*/true, &n_signed, m_transaction_data, complete)};
+    const auto err{m_wallet_model->wallet().fillPSBT(SIGHASH_DEFAULT, /*sign=*/true, /*bip32derivs=*/true, &n_signed, m_transaction_data, complete)};
 
     if (err) {
         showStatus(tr("Failed to sign transaction: %1")