Enable Server Tests on Windows

[jtpio]

Windows Terminal tests were disabled in #201, but can now be enabled based on improvements in pywinpty 1.1. Also fixes test failure introduced in #504

[codecov-commenter]

Codecov Report

Merging #519 (3216dbe) into master (6bf5914) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #519      +/-   ##
==========================================
+ Coverage   76.99%   77.03%   +0.04%     
==========================================
  Files         107      107              
  Lines        9511     9511              
  Branches     1032     1031       -1     
==========================================
+ Hits         7323     7327       +4     
+ Misses       1815     1813       -2     
+ Partials      373      371       -2     

Impacted Files	Coverage Δ
jupyter_server/services/config/manager.py	100.00% <ø> (ø)
jupyter_server/tests/extension/test_manager.py	100.00% <100.00%> (ø)
jupyter_server/tests/test_terminal.py	98.80% <100.00%> (+2.33%)	⬆️
jupyter_server/services/kernels/kernelmanager.py	80.79% <0.00%> (+0.72%)	⬆️

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[blink1073]

Thanks!