Stabilized test_mutable_errback_called_by_chord_from_group_fail_multiple

[Nusnus]

test_mutable_errback_called_by_chord_from_group_fail_multiple was failing randomly for some time now.
I suspect the arbitrary task count used in the test was too high so I lowered it from 24 to 8.
PR Opened due to Issue #7836

[codecov]

Codecov Report

Base: 89.77% // Head: 89.77% // No change to project coverage 👍

Coverage data is based on head (89db817) compared to base (7d4fe22).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7837   +/-   ##
=======================================
  Coverage   89.77%   89.77%           
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  Files         128      128           
  Lines       15790    15790           
  Branches     2111     2111           
=======================================
  Hits        14176    14176           
  Misses       1386     1386           
  Partials      228      228           

Flag	Coverage Δ
unittests	89.75% <ø> (ø)

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[auvipy]

one version is still showing timeout error

[Nusnus]

I am trying to play with more arbitrary values in the test. Let's see if it works.

[Nusnus]

The test had two different cases implemented under one roof. I'm trying to separate it for a test per (logical) case, hoping it would reduce the effort of each test and hopefully will make it stable.

As of making this comment, it seems my fix works.

I will re-run all of the automatic tests a few times in a row, just for fun, to see if the fix is deterministic or if I just had "luck" this run.

[Nusnus]

I want to believe 3 successful runs in a row is good enough, what do you say @auvipy ?