Fix signing requirement against signing required

[laxa]

When using smbprotocol, with require_signing=False on the Connection class, against a computer requiring signing (a Domain Controller for example), the client fails to update its client_security_mode as stated in the specification section 3.2.4.2.2.2.

EDIT: force pushed to update test case that failed with the initial PR

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.78%. Comparing base (9b8e7d4) to head (01ff473).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #356   +/-   ##
=======================================
  Coverage   98.78%   98.78%           
=======================================
  Files          24       24           
  Lines        5276     5277    +1     
=======================================
+ Hits         5212     5213    +1     
  Misses         64       64           

Flag	Coverage Δ
macOS	68.20% <0.00%> (-0.02%)	⬇️
py3.10	98.78% <100.00%> (+<0.01%)	⬆️
py3.11	98.78% <100.00%> (+<0.01%)	⬆️
py3.12	98.78% <100.00%> (+<0.01%)	⬆️
py3.13	98.78% <100.00%> (+<0.01%)	⬆️
py3.14	98.78% <100.00%> (+<0.01%)	⬆️
ubuntu	96.62% <100.00%> (+<0.01%)	⬆️
windows	98.71% <100.00%> (+<0.01%)	⬆️

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