Merge #21712: qa: Test default include_mempool value of gettxout

44dab423eb qa: Test default include_mempool value of gettxout (João Barbosa)

Pull request description:

  With the following diff the functional test would pass. Fix by testing the default value.

  ```diff
  --- a/src/rpc/blockchain.cpp
  +++ b/src/rpc/blockchain.cpp
  @@ -1142,7 +1142,7 @@ static RPCHelpMan gettxout()
       uint256 hash(ParseHashV(request.params[0], "txid"));
       int n = request.params[1].get_int();
       COutPoint out(hash, n);
  -    bool fMempool = true;
  +    bool fMempool = false;
       if (!request.params[2].isNull())
           fMempool = request.params[2].get_bool();
  ```

ACKs for top commit:
  MarcoFalke:
    cr ACK 44dab423eb

Tree-SHA512: 14db21b29d6b2c01d1d1278e18a0cf35d6ae566e33e45515d1fe2983dda94ad1ff6065c217601d283f9515cae39b57e981b62ac71ec2002de5359bd8a9e3efa9

test/functional/wallet_basic.py

@@ -95,6 +95,8 @@ class WalletTest(BitcoinTestFramework):
         # but invisible if you include mempool
         txout = self.nodes[0].gettxout(confirmed_txid, confirmed_index, False)
         assert_equal(txout['value'], 50)
+        txout = self.nodes[0].gettxout(confirmed_txid, confirmed_index)  # by default include_mempool=True
+        assert txout is None
         txout = self.nodes[0].gettxout(confirmed_txid, confirmed_index, True)
         assert txout is None
         # new utxo from mempool should be invisible if you exclude mempool