flaky network tests on Windows

[jelmer]

Some of the network tests appear to be flaky on windows, and fairly regularly fail:

 ======================================================================
ERROR: test_fetch_pack (dulwich.tests.compat.test_client.DulwichTCPClientTest)
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Traceback (most recent call last):
  File "D:\a\dulwich\dulwich\dulwich\protocol.py", line 230, in read_pkt_line
    sizestr = read(4)
  File "C:\hostedtoolcache\windows\Python\3.10.6\x64\lib\socket.py", line 705, in readinto
    return self._sock.recv_into(b)
ConnectionResetError: [WinError 10054] An existing connection was forcibly closed by the remote host

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "D:\a\dulwich\dulwich\dulwich\tests\compat\test_client.py", line 238, in test_fetch_pack
    result = c.fetch(self._build_path("/server_new.export"), dest)
  File "D:\a\dulwich\dulwich\dulwich\client.py", line 837, in fetch
    result = self.fetch_pack(
  File "D:\a\dulwich\dulwich\dulwich\client.py", line 1183, in fetch_pack
    _handle_upload_pack_tail(
  File "D:\a\dulwich\dulwich\dulwich\client.py", line 629, in _handle_upload_pack_tail
    _read_side_band64k_data(
  File "D:\a\dulwich\dulwich\dulwich\client.py", line 509, in _read_side_band64k_data
    for pkt in pkt_seq:
  File "D:\a\dulwich\dulwich\dulwich\protocol.py", line 290, in read_pkt_seq
    pkt = self.read_pkt_line()
  File "D:\a\dulwich\dulwich\dulwich\protocol.py", line 242, in read_pkt_line
    raise GitProtocolError(e)
dulwich.errors.GitProtocolError: [WinError 10054] An existing connection was forcibly closed by the remote host

[jelmer]

From what I can tell, this is specific to the TCP Client and it might not be isolated to Windows (though more likely to be triggered there).