Fix behaviour of async PythonParser to match RedisParser as for issue #2349

[kristjanvalur]

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Description of change

PR #2557 we allowed the async HiredisParser to finish reading a response even while a concurrent disconnect() might be issued. This PR enables the test, and duplicates the behaviour for the PythonParser.

[codecov-commenter]

Codecov Report

Patch coverage: 81.81% and project coverage change: +0.04 🎉

Comparison is base (7d474f9) 60.38% compared to head (07c2c1d) 60.42%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2582      +/-   ##
==========================================
+ Coverage   60.38%   60.42%   +0.04%     
==========================================
  Files         115      115              
  Lines       29725    29750      +25     
==========================================
+ Hits        17949    17977      +28     
+ Misses      11776    11773       -3     

Impacted Files	Coverage Δ
tests/test_asyncio/test_connection.py	39.35% <ø> (+0.50%)	⬆️
redis/asyncio/connection.py	81.67% <81.81%> (ø)

... and 25 files with indirect coverage changes

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[kristjanvalur]

Some of our tests are quite finnicky, sensitive to timeouts occurring which can always happein in a virtualized backend.

[dvora-h]

@kristjanvalur Can you resolve the conflicts?