qa: test that we do disconnect upon a second invalid compact block being announced

This was in fact untested until now. This can be checked with the following diff.

```diff
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 0c4a89c44cb..f8b9adf910a 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -1822,7 +1822,7 @@ void PeerManagerImpl::MaybePunishNodeForBlock(NodeId nodeid, const BlockValidati
         }
     case BlockValidationResult::BLOCK_INVALID_HEADER:
     case BlockValidationResult::BLOCK_INVALID_PREV:
-        if (peer) Misbehaving(*peer, message);
+        if (!via_compact_block && peer) Misbehaving(*peer, message);
         return;
     // Conflicting (but not necessarily invalid) data or different policy:
     case BlockValidationResult::BLOCK_MISSING_PREV:
```

test/functional/p2p_compactblocks.py

@@ -751,6 +751,13 @@ class CompactBlocksTest(BitcoinTestFramework):
         assert_not_equal(node.getbestblockhash(), block.hash_hex)
         test_node.sync_with_ping()
 
+        # Now, announcing a second block building on top of the invalid one will get us disconnected.
+        block.hashPrevBlock = block.hash_int
+        block.solve()
+        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_await_disconnect(msg)
+
     # Helper for enabling cb announcements
     # Send the sendcmpct request and sync headers
     def request_cb_announcements(self, peer):
@@ -967,6 +974,9 @@ class CompactBlocksTest(BitcoinTestFramework):
         self.log.info("Testing handling of invalid compact blocks...")
         self.test_invalid_tx_in_compactblock(self.segwit_node)
 
+        # The previous test will lead to a disconnection. Reconnect before continuing.
+        self.segwit_node = self.nodes[0].add_p2p_connection(TestP2PConn())
+
         self.log.info("Testing invalid index in cmpctblock message...")
         self.test_invalid_cmpctblock_message()