Merge bitcoin/bitcoin#22809: test: Check that non-signaling BIP125 tx can be replaced via parent

fa2e9de59f test: Check that non-signaling BIP125 tx can be replaced via parent (MarcoFalke)

Pull request description:

  While `optout_child_tx` in the `test_no_inherited_signaling` test is reported as "bip125-replaceable", it is not *directly* replaceable. For example by bumping the fee of `optout_child_tx`. However, it is still replaceable *indirectly* via it's BIP-125 signalling parent.

  Clarify this by extending the test.

ACKs for top commit:
  mjdietzx:
    Tested ACK fa2e9de59f
  josibake:
    ACK fa2e9de59f

Tree-SHA512: b3608beae743dcb6152df4d2cfe1c0af6b4404ba3837f73e1d1431bd7c637f0c7fab0379aaab2218d5cd63e71070a079c0595ec031056058e8d3c933c2bae0a9

test/functional/feature_rbf.py

@@ -618,6 +618,17 @@ class ReplaceByFeeTest(BitcoinTestFramework):
         assert_equal(True, self.nodes[0].getmempoolentry(optin_parent_tx['txid'])['bip125-replaceable'])
         assert_raises_rpc_error(-26, 'txn-mempool-conflict', self.nodes[0].sendrawtransaction, replacement_child_tx["hex"], 0)
 
+        self.log.info('Check that the child tx can still be replaced (via a tx that also replaces the parent)')
+        replacement_parent_tx = self.wallet.send_self_transfer(
+            from_node=self.nodes[0],
+            utxo_to_spend=confirmed_utxo,
+            sequence=0xffffffff,
+            fee_rate=Decimal('0.03'),
+        )
+        # Check that child is removed and update wallet utxo state
+        assert_raises_rpc_error(-5, 'Transaction not in mempool', self.nodes[0].getmempoolentry, optout_child_tx['txid'])
+        self.wallet.get_utxo(txid=optout_child_tx['txid'])
+
     def test_replacement_relay_fee(self):
         tx = self.wallet.send_self_transfer(from_node=self.nodes[0])['tx']