Slightly improve tests execution time

[popravich]

What do these changes do?

Slightly improve tests running time

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• Add a new news fragment into the CHANGES/ folder

[codecov]

Codecov Report

Merging #643 into master will decrease coverage by 16.84%.
The diff coverage is 69.49%.

@@            Coverage Diff            @@
##           master   #643       +/-   ##
=========================================
- Coverage   96.85%    80%   -16.85%     
=========================================
  Files          57     57               
  Lines        8551   8049      -502     
  Branches      578    570        -8     
=========================================
- Hits         8282   6440     -1842     
- Misses        192   1555     +1363     
+ Partials       77     54       -23

Impacted Files	Coverage Δ
tests/_testutils.py	100% <ø> (+15.78%)	⬆️
tests/stream_commands_test.py	16.21% <ø> (-83.79%)	⬇️
tests/conftest.py	55.05% <0%> (-34.43%)	⬇️
tests/pubsub_receiver_test.py	98.82% <100%> (-0.04%)	⬇️
tests/pubsub_commands_test.py	96.46% <100%> (-3.54%)	⬇️
tests/generic_commands_test.py	85.02% <100%> (-14.98%)	⬇️
tests/pool_test.py	96.74% <100%> (-2.99%)	⬇️
tests/server_commands_test.py	92.09% <100%> (-7.91%)	⬇️
tests/sentinel_commands_test.py	18.82% <33.33%> (-81.18%)	⬇️
tests/sentinel_failover_test.py	12.8% <7.69%> (-75.06%)	⬇️
... and 43 more

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