Patch asyncio event loop policy on windows

[philippjfr]

Reference bokeh/bokeh#12018 and tornadoweb/tornado#2608

[codecov]

Codecov Report

Merging #3339 (28f773f) into master (e52b8c0) will decrease coverage by 0.00%.
The diff coverage is 57.14%.

@@            Coverage Diff             @@
##           master    #3339      +/-   ##
==========================================
- Coverage   83.40%   83.40%   -0.01%     
==========================================
  Files         196      196              
  Lines       26559    26565       +6     
==========================================
+ Hits        22152    22156       +4     
- Misses       4407     4409       +2     

Impacted Files	Coverage Δ
panel/io/server.py	78.30% <57.14%> (-0.16%)	⬇️
panel/template/base.py	77.09% <0.00%> (ø)

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