test(ioredis): make flaky test deterministic

[blumamir]

Which problem is this PR solving?

fixes #332
The test should create a child span for pubsub in ioredis plugin and instrumentation is creating two clients that send Redis commands asynchronously, which makes the output nondeterministic.

Short description of the changes

Make the test synchronously and deterministic by awaiting the connect function of each client before continuing to the following operations.

[codecov]

Codecov Report

Merging #342 (40cbbb8) into main (c8b7f3d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #342   +/-   ##
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  Coverage   93.88%   93.88%           
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  Files          12       12           
  Lines         409      409           
  Branches       45       45           
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  Hits          384      384           
  Misses         25       25