test: Add missing sync on send_version in peer_connect #28782

Without the sync, the logic will be racy. For example, p2p_sendtxrcncl.py is failing locally (and on CI occasionally), because non-version messages will be sent before the version message:

        self.log.info('SENDTXRCNCL with version=0 triggers a disconnect')
        sendtxrcncl_low_version = create_sendtxrcncl_msg()
        sendtxrcncl_low_version.version = 0
        peer = self.nodes[0].add_p2p_connection(PeerNoVerack(), send_version=True, wait_for_verack=False)
        with self.nodes[0].assert_debug_log(["txreconciliation protocol violation"]):
            peer.send_message(sendtxrcncl_low_version)
            peer.wait_for_disconnect()

 test  2023-11-02T08:15:19.620000Z TestFramework (INFO): SENDTXRCNCL with version=0 triggers a disconnect 
 test  2023-11-02T08:15:19.621000Z TestFramework.p2p (DEBUG): Connecting to Bitcoin Node: 127.0.0.1:11312 
 test  2023-11-02T08:15:19.624000Z TestFramework.p2p (DEBUG): Connected & Listening: 127.0.0.1:11312 
 test  2023-11-02T08:15:19.798000Z TestFramework.p2p (DEBUG): Send message to 127.0.0.1:11312: msg_sendtxrcncl(version=0, salt=2) 
 test  2023-11-02T08:15:19.799000Z TestFramework.p2p (DEBUG): Send message to 127.0.0.1:11312: msg_version(nVersion=70016 nServices=9 nTime=Thu Nov  2 08:15:19 2023 addrTo=CAddress(nServices=1 net=IPv4 addr=127.0.0.1 port=11312) addrFrom=CAddress(nServices=1 net=IPv4 addr=0.0.0.0 port=0) nNonce=0x369AC031CDA96022 strSubVer=/python-p2p-tester:0.0.3/ nStartingHeight=-1 relay=1) 
 node0 2023-11-02T08:15:19.804409Z [net] [net.cpp:3676] [CNode] [net] Added connection peer=0 
 node0 2023-11-02T08:15:19.805256Z [net] [net.cpp:1825] [CreateNodeFromAcceptedSocket] [net] connection from 127.0.0.1:55964 accepted 
 node0 2023-11-02T08:15:19.809861Z [msghand] [net_processing.cpp:3356] [ProcessMessage] [net] received: sendtxrcncl (12 bytes) peer=0 
 node0 2023-11-02T08:15:19.810297Z [msghand] [net_processing.cpp:3582] [ProcessMessage] [net] non-version message before version handshake. Message "sendtxrcncl" from peer=0 
 node0 2023-11-02T08:15:19.810928Z [msghand] [net_processing.cpp:3356] [ProcessMessage] [net] received: version (111 bytes) peer=0 
...
 test  2023-11-02T09:35:20.166000Z TestFramework.utils (ERROR): wait_until() failed. Predicate: '''' 
                                           def test_function():
                                               if check_connected:
                                                   assert self.is_connected
                                               return test_function_in()
                                   '''
 test  2023-11-02T09:35:20.187000Z TestFramework (ERROR): Assertion failed 
                                   Traceback (most recent call last):
                                     File "/ci_container_base/ci/scratch/build/bitcoin-s390x-linux-gnu/test/functional/test_framework/test_framework.py", line 132, in main
                                       self.run_test()
                                     File "/ci_container_base/ci/scratch/build/bitcoin-s390x-linux-gnu/test/functional/p2p_sendtxrcncl.py", line 188, in run_test
                                       peer.wait_for_disconnect()
                                     File "/ci_container_base/ci/scratch/build/bitcoin-s390x-linux-gnu/test/functional/test_framework/p2p.py", line 478, in wait_for_disconnect
                                       self.wait_until(test_function, timeout=timeout, check_connected=False)
                                     File "/ci_container_base/ci/scratch/build/bitcoin-s390x-linux-gnu/test/functional/test_framework/p2p.py", line 470, in wait_until
                                       wait_until_helper_internal(test_function, timeout=timeout, lock=p2p_lock, timeout_factor=self.timeout_factor)
                                     File "/ci_container_base/ci/scratch/build/bitcoin-s390x-linux-gnu/test/functional/test_framework/util.py", line 275, in wait_until_helper_internal
                                       raise AssertionError("Predicate {} not true after {} seconds".format(predicate_source, timeout))
                                   AssertionError: Predicate ''''
                                           def test_function():
                                               if check_connected:
                                                   assert self.is_connected
                                               return test_function_in()
                                   ''' not true after 4800.0 seconds

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #28463 (p2p: Increase inbound capacity for block-relay only connections by mzumsande)
• #24748 (test/BIP324: functional tests for v2 P2P encryption by stratospher)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

ACK fa025984698270d8c9a621aef80f1d788ea2ab2e

I tested this by adding a sleep to connection_made before sending the message. However p2p_sendtxrcncl.py will then fail later in the SENDTXRCNCL if block-relay-only triggers a disconnect part because add_outbound_p2p_connection has the same problem. Do you want to fix that too here, or in another PR?