qa: test a compact block with an invalid transaction

The current test to exercise a block with an invalid transaction actually
creates a block with an invalid coinbase witness, which is checked early and
for which MaybePunishNodeForBlock() is not called.

Add a test case with an invalid regular transaction, which will lead
CheckInputScripts to return a CONSENSUS error and MaybePunishNodeForBlock() to
be called, appropriately not disconnecting upon an invalid compact block. This
was until now untested as can be checked with the following diff:
```diff
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 0c4a89c..d243fb88d4b 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -1805,10 +1805,10 @@ void PeerManagerImpl::MaybePunishNodeForBlock(NodeId nodeid, const BlockValidati
     // The node is providing invalid data:
     case BlockValidationResult::BLOCK_CONSENSUS:
     case BlockValidationResult::BLOCK_MUTATED:
-        if (!via_compact_block) {
+        //if (!via_compact_block) {
             if (peer) Misbehaving(*peer, message);
             return;
-        }
+        //}
         break;
     case BlockValidationResult::BLOCK_CACHED_INVALID:
         {
```

Finally, note this failure is cached (unlike the malleated witness failure),
which will be used in the following commits.

Author: darosior

test/functional/p2p_compactblocks.py

@@ -54,6 +54,7 @@
     CScript,
     OP_DROP,
     OP_TRUE,
+    OP_RETURN,
 )
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
@@ -726,6 +727,23 @@ def test_invalid_tx_in_compactblock(self, test_node):
         assert_not_equal(node.getbestblockhash(), block.hash_hex)
         test_node.sync_with_ping()
 
+        # Re-establish a proper witness commitment with the coinbase witness, but
+        # invalidate the last tx in the block.
+        block.vtx[4].vin[0].scriptSig = CScript([OP_RETURN])
+        block.hashMerkleRoot = block.calc_merkle_root()
+        add_witness_commitment(block)
+        block.solve()
+
+        # This will lead to a consensus failure for which we also won't be disconnected but which
+        # will be cached.
+        comp_block.initialize_from_block(block, prefill_list=list(range(len(block.vtx))), use_witness=True)
+        msg = msg_cmpctblock(comp_block.to_p2p())
+        test_node.send_and_ping(msg)
+
+        # The tip still didn't advance.
+        assert_not_equal(node.getbestblockhash(), block.hash_hex)
+        test_node.sync_with_ping()
+
     # Helper for enabling cb announcements
     # Send the sendcmpct request and sync headers
     def request_cb_announcements(self, peer):