DEV: add php-pcntl as dependency to composer

[TonisOrmisson]

got an exeption in one system from here

yii2-queue/src/ProcessRunner.php

Lines 341 to 342 in 9007970

	pcntl_signal(SIGTERM, $signalHandler);
	pcntl_signal(SIGINT, $signalHandler);

[codecov]

Codecov Report

Merging #81 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #81      +/-   ##
==========================================
+ Coverage   70.21%   70.22%   +<.01%     
==========================================
  Files          15       15              
  Lines         695      628      -67     
==========================================
- Hits          488      441      -47     
+ Misses        207      187      -20

Impacted Files	Coverage Δ
...rc/Behaviors/ActiveRecordDeferredEventBehavior.php	38.88% <0%> (-1.47%)	⬇️
...viors/ActiveRecordDeferredEventRoutingBehavior.php	89.47% <0%> (-1.01%)	⬇️
src/Behaviors/DeferredEventBehavior.php	66.66% <0%> (-0.61%)	⬇️
src/Queues/MemoryQueue.php	84.61% <0%> (-0.57%)	⬇️
src/Queues/RedisQueue.php	85.71% <0%> (-0.5%)	⬇️
src/Queue.php	83.87% <0%> (-0.46%)	⬇️
src/Strategies/Strategy.php	45% <0%> (-0.46%)	⬇️
src/Queues/DbQueue.php	86.66% <0%> (-0.22%)	⬇️
src/Behaviors/DeferredEventHandler.php	100% <0%> (ø)	⬆️
src/Behaviors/DeferredEventRoutingBehavior.php	100% <0%> (ø)	⬆️
... and 4 more

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